I was investigating the following crash where a checkpoint task had its
underlying resources being destroyed while it was still running. The two
interesting threads are the following:

```
thread #1, name = 'duckling', stop reason = signal SIGTRAP
    frame #0: 0x0000ffff91bb71ec
    frame #1: 0x0000aaaad73a38e8 duckling`duckdb::InternalException::InternalException(this=<unavailable>, msg=<unavailable>) at exception.cpp:336:2
    frame #2: 0x0000aaaad786eb68 duckling`duckdb::unique_ptr<duckdb::RowGroup, std::default_delete<duckdb::RowGroup>, true>::operator*() const [inlined] duckdb::unique_ptr<duckdb::RowGroup, std::default_delete<duckdb::RowGroup>, true>::AssertNotNull(null=<unavailable>) at unique_ptr.hpp:25:10
    frame #3: 0x0000aaaad786eaf4 duckling`duckdb::unique_ptr<duckdb::RowGroup, std::default_delete<duckdb::RowGroup>, true>::operator*(this=0x0000aaacbb73e008) const at unique_ptr.hpp:34:4
    frame #4: 0x0000aaaad787abbc duckling`duckdb::CheckpointTask::ExecuteTask(this=0x0000aaabec92be60) at row_group_collection.cpp:732:21
    frame #5: 0x0000aaaad7756ea4 duckling`duckdb::BaseExecutorTask::Execute(this=0x0000aaabec92be60, mode=<unavailable>) at task_executor.cpp:72:3
    frame #6: 0x0000aaaad7757e28 duckling`duckdb::TaskScheduler::ExecuteForever(this=0x0000aaaafda30e10, marker=0x0000aaaafda164a8) at task_scheduler.cpp:189:32
    frame #7: 0x0000ffff91a031fc
    frame #8: 0x0000ffff91c0d5c8

thread duckdb#120, stop reason = signal 0
    frame #0: 0x0000ffff91c71c24
    frame #1: 0x0000ffff91e1264c
    frame #2: 0x0000ffff91e01888
    frame #3: 0x0000ffff91e018f8
    frame #4: 0x0000ffff91e01c10
    frame #5: 0x0000ffff91e05afc
    frame #6: 0x0000ffff91e05e70
    frame #7: 0x0000aaaad784b63c duckling`duckdb::RowGroup::~RowGroup() [inlined] std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release(this=<unavailable>) at shared_ptr_base.h:184:10
    frame #8: 0x0000aaaad784b5b4 duckling`duckdb::RowGroup::~RowGroup() [inlined] std::__shared_count<(__gnu_cxx::_Lock_policy)2>::~__shared_count(this=<unavailable>) at shared_ptr_base.h:705:11
    frame #9: 0x0000aaaad784b5ac duckling`duckdb::RowGroup::~RowGroup() [inlined] std::__shared_ptr<duckdb::ColumnData, (__gnu_cxx::_Lock_policy)2>::~__shared_ptr(this=<unavailable>) at shared_ptr_base.h:1154:31
    frame #10: 0x0000aaaad784b5ac duckling`duckdb::RowGroup::~RowGroup() [inlined] duckdb::shared_ptr<duckdb::ColumnData, true>::~shared_ptr(this=<unavailable>) at shared_ptr_ipp.hpp:115:24
    frame #11: 0x0000aaaad784b5ac duckling`duckdb::RowGroup::~RowGroup() [inlined] void std::_Destroy<duckdb::shared_ptr<duckdb::ColumnData, true>>(__pointer=<unavailable>) at stl_construct.h:151:19
    frame #12: 0x0000aaaad784b5ac duckling`duckdb::RowGroup::~RowGroup() [inlined] void std::_Destroy_aux<false>::__destroy<duckdb::shared_ptr<duckdb::ColumnData, true>*>(__first=<unavailable>, __last=<unavailable>) at stl_construct.h:163:6
    frame #13: 0x0000aaaad784b5a0 duckling`duckdb::RowGroup::~RowGroup() [inlined] void std::_Destroy<duckdb::shared_ptr<duckdb::ColumnData, true>*>(__first=<unavailable>, __last=<unavailable>) at stl_construct.h:195:7
    frame #14: 0x0000aaaad784b5a0 duckling`duckdb::RowGroup::~RowGroup() [inlined] void std::_Destroy<duckdb::shared_ptr<duckdb::ColumnData, true>*, duckdb::shared_ptr<duckdb::ColumnData, true>>(__first=<unavailable>, __last=<unavailable>, (null)=<unavailable>) at alloc_traits.h:848:7
    frame #15: 0x0000aaaad784b5a0 duckling`duckdb::RowGroup::~RowGroup() [inlined] std::vector<duckdb::shared_ptr<duckdb::ColumnData, true>, std::allocator<duckdb::shared_ptr<duckdb::ColumnData, true>>>::~vector(this=<unavailable>) at stl_vector.h:680:2
    frame #16: 0x0000aaaad784b5a0 duckling`duckdb::RowGroup::~RowGroup(this=<unavailable>) at row_group.cpp:83:1
    frame #17: 0x0000aaaad786ee18 duckling`std::vector<duckdb::SegmentNode<duckdb::RowGroup>, std::allocator<duckdb::SegmentNode<duckdb::RowGroup>>>::~vector() [inlined] std::default_delete<duckdb::RowGroup>::operator()(this=0x0000aaacbb73e1a8, __ptr=0x0000aaab75ae7860) const at unique_ptr.h:85:2
    frame #18: 0x0000aaaad786ee10 duckling`std::vector<duckdb::SegmentNode<duckdb::RowGroup>, std::allocator<duckdb::SegmentNode<duckdb::RowGroup>>>::~vector() at unique_ptr.h:361:4
    frame #19: 0x0000aaaad786ee08 duckling`std::vector<duckdb::SegmentNode<duckdb::RowGroup>, std::allocator<duckdb::SegmentNode<duckdb::RowGroup>>>::~vector() [inlined] duckdb::SegmentNode<duckdb::RowGroup>::~SegmentNode(this=0x0000aaacbb73e1a0) at segment_tree.hpp:21:8
    frame #20: 0x0000aaaad786ee08 duckling`std::vector<duckdb::SegmentNode<duckdb::RowGroup>, std::allocator<duckdb::SegmentNode<duckdb::RowGroup>>>::~vector() [inlined] void std::_Destroy<duckdb::SegmentNode<duckdb::RowGroup>>(__pointer=0x0000aaacbb73e1a0) at stl_construct.h:151:19
    frame #21: 0x0000aaaad786ee08 duckling`std::vector<duckdb::SegmentNode<duckdb::RowGroup>, std::allocator<duckdb::SegmentNode<duckdb::RowGroup>>>::~vector() [inlined] void std::_Destroy_aux<false>::__destroy<duckdb::SegmentNode<duckdb::RowGroup>*>(__first=0x0000aaacbb73e1a0, __last=0x0000aaacbb751130) at stl_construct.h:163:6
    frame #22: 0x0000aaaad786ede8 duckling`std::vector<duckdb::SegmentNode<duckdb::RowGroup>, std::allocator<duckdb::SegmentNode<duckdb::RowGroup>>>::~vector() [inlined] void std::_Destroy<duckdb::SegmentNode<duckdb::RowGroup>*>(__first=<unavailable>, __last=0x0000aaacbb751130) at stl_construct.h:195:7
    frame #23: 0x0000aaaad786ede8 duckling`std::vector<duckdb::SegmentNode<duckdb::RowGroup>, std::allocator<duckdb::SegmentNode<duckdb::RowGroup>>>::~vector() [inlined] void std::_Destroy<duckdb::SegmentNode<duckdb::RowGroup>*, duckdb::SegmentNode<duckdb::RowGroup>>(__first=<unavailable>, __last=0x0000aaacbb751130, (null)=0x0000fffefc81a908) at alloc_traits.h:848:7
    frame #24: 0x0000aaaad786ede8 duckling`std::vector<duckdb::SegmentNode<duckdb::RowGroup>, std::allocator<duckdb::SegmentNode<duckdb::RowGroup>>>::~vector(this=size=4883) at stl_vector.h:680:2
    frame #25: 0x0000aaaad7857f74 duckling`duckdb::RowGroupCollection::Checkpoint(this=<unavailable>, writer=<unavailable>, global_stats=0x0000fffefc81a9c0) at row_group_collection.cpp:1017:1
    frame #26: 0x0000aaaad788f02c duckling`duckdb::DataTable::Checkpoint(this=0x0000aaab04649e70, writer=0x0000aaab6584ea80, serializer=0x0000fffefc81ab38) at data_table.cpp:1427:14
    frame #27: 0x0000aaaad7881394 duckling`duckdb::SingleFileCheckpointWriter::WriteTable(this=0x0000fffefc81b128, table=0x0000aaab023b78c0, serializer=0x0000fffefc81ab38) at checkpoint_manager.cpp:528:11
    frame #28: 0x0000aaaad787ece4 duckling`duckdb::SingleFileCheckpointWriter::CreateCheckpoint() [inlined] duckdb::SingleFileCheckpointWriter::CreateCheckpoint(this=<unavailable>, obj=0x0000fffefc81ab38)::$_7::operator()(duckdb::Serializer::List&, unsigned long) const::'lambda'(duckdb::Serializer&)::operator()(duckdb::Serializer&) const at checkpoint_manager.cpp:181:43
    frame #29: 0x0000aaaad787ecd8 duckling`duckdb::SingleFileCheckpointWriter::CreateCheckpoint() [inlined] void duckdb::Serializer::List::WriteObject<duckdb::SingleFileCheckpointWriter::CreateCheckpoint()::$_7::operator()(duckdb::Serializer::List&, unsigned long) const::'lambda'(duckdb::Serializer&)>(this=<unavailable>, f=(unnamed class) @ 0x0000600002cbd2b0) at serializer.hpp:385:2
    frame #30: 0x0000aaaad787ecc4 duckling`duckdb::SingleFileCheckpointWriter::CreateCheckpoint() [inlined] duckdb::SingleFileCheckpointWriter::CreateCheckpoint()::$_7::operator()(this=<unavailable>, list=<unavailable>, i=2) const at checkpoint_manager.cpp:181:8
    frame #31: 0x0000aaaad787ecb0 duckling`duckdb::SingleFileCheckpointWriter::CreateCheckpoint() at serializer.hpp:151:4
    frame #32: 0x0000aaaad787ec94 duckling`duckdb::SingleFileCheckpointWriter::CreateCheckpoint(this=0x0000fffefc81b128) at checkpoint_manager.cpp:179:13
    frame #33: 0x0000aaaad78954a8 duckling`duckdb::SingleFileStorageManager::CreateCheckpoint(this=0x0000aaaafe1de140, options=(wal_action = DONT_DELETE_WAL, action = CHECKPOINT_IF_REQUIRED, type = FULL_CHECKPOINT)) at storage_manager.cpp:365:17
    frame #34: 0x0000aaaad78baac0 duckling`duckdb::DuckTransactionManager::Checkpoint(this=0x0000aaaafe167e00, context=<unavailable>, force=<unavailable>) at duck_transaction_manager.cpp:198:18
    frame #35: 0x0000aaaad69d02c0 duckling`md::Server::BackgroundCheckpointIfNeeded(this=0x0000aaaafdbfe900) at server.cpp:1983:31
    frame #36: 0x0000aaaadac5d3f0 duckling`std::thread::_State_impl<std::thread::_Invoker<std::tuple<md::BackgroundCronTask::Start(unsigned long)::$_0>>>::_M_run() [inlined] std::function<void ()>::operator()(this=<unavailable>) const at std_function.h:590:9
    frame #37: 0x0000aaaadac5d3e0 duckling`std::thread::_State_impl<std::thread::_Invoker<std::tuple<md::BackgroundCronTask::Start(unsigned long)::$_0>>>::_M_run() [inlined] md::BackgroundCronTask::Start(unsigned long)::$_0::operator()(this=0x0000aaaafdf169a8) const at background_cron_task.cpp:25:4
    frame #38: 0x0000aaaadac5d30c duckling`std::thread::_State_impl<std::thread::_Invoker<std::tuple<md::BackgroundCronTask::Start(unsigned long)::$_0>>>::_M_run() [inlined] void std::__invoke_impl<void, md::BackgroundCronTask::Start(unsigned long)::$_0>((null)=<unavailable>, __f=0x0000aaaafdf169a8) at invoke.h:61:14
    frame #39: 0x0000aaaadac5d30c duckling`std::thread::_State_impl<std::thread::_Invoker<std::tuple<md::BackgroundCronTask::Start(unsigned long)::$_0>>>::_M_run() [inlined] std::__invoke_result<md::BackgroundCronTask::Start(unsigned long)::$_0>::type std::__invoke<md::BackgroundCronTask::Start(unsigned long)::$_0>(__fn=0x0000aaaafdf169a8) at invoke.h:96:14
    frame #40: 0x0000aaaadac5d30c duckling`std::thread::_State_impl<std::thread::_Invoker<std::tuple<md::BackgroundCronTask::Start(unsigned long)::$_0>>>::_M_run() [inlined] void std::thread::_Invoker<std::tuple<md::BackgroundCronTask::Start(unsigned long)::$_0>>::_M_invoke<0ul>(this=0x0000aaaafdf169a8, (null)=<unavailable>) at std_thread.h:259:13
    frame #41: 0x0000aaaadac5d30c duckling`std::thread::_State_impl<std::thread::_Invoker<std::tuple<md::BackgroundCronTask::Start(unsigned long)::$_0>>>::_M_run() [inlined] std::thread::_Invoker<std::tuple<md::BackgroundCronTask::Start(unsigned long)::$_0>>::operator()(this=0x0000aaaafdf169a8) at std_thread.h:266:11
    frame #42: 0x0000aaaadac5d30c duckling`std::thread::_State_impl<std::thread::_Invoker<std::tuple<md::BackgroundCronTask::Start(unsigned long)::$_0>>>::_M_run(this=0x0000aaaafdf169a0) at std_thread.h:211:13
    frame #43: 0x0000ffff91a031fc
    frame #44: 0x0000ffff91c0d5c8
```

The problem is that if there's an IO exception being thrown in
`RowGroupCollection::Checkpoint` after some (but not all) checkpoint
tasks have been scheduled but before
`checkpoint_state.executor.WorkOnTasks();` is called, it results in an
InternalException / DuckDB crash as the `Checkpoint ` method does not
wait for the scheduled tasks to have completed before destroying the
referenced resources.

…groups, and limiting vacuum operations for the last number of row groups (duckdb#18829)

When performing a checkpoint, we rewrite columns of row groups that have
had modifications. When performing insertions, all columns are modified,
thus all columns of a row group must be rewritten. As a result, any
insertion followed by a checkpoint triggers a full rewrite of the last
row group.

When dealing with wide tables or string columns with large strings,
rewriting a row group can be relatively expensive. This is particularly
the case when only small insertions have been made. For example,
inserting a single row followed by checkpointing can become expensive as
a result of triggering a rewrite of the last row group:

```sql
create table z as select repeat(sha256(i::varchar), 10) as a, repeat(sha256((i**2)::varchar), 10) as b, repeat(sha256((i**3)::varchar), 10) as c from range(100000) r(i);
CHECKPOINT;
.timer on
insert into z values ('a','b','c');
Run Time (s): real 0.006 user 0.004249 sys 0.001186
CHECKPOINT;
Run Time (s): real 0.611 user 1.163009 sys 0.054814
```

The checkpoint takes 0.6s, despite us inserting only a single row.

#### Appending a new row group

This PR solves this problem by appending a new row group when writing to
a table that has been persisted/checkpointed. As a result, we will no
longer modify the (already checkpointed) data. As a trade-off, we end up
with more (smaller) row groups.

#### Vacuuming
As part of vacuuming, we merge adjacent row groups if they fit within
the row group size. As part of this PR - we restrict merging for the
last few row groups. Otherwise, we would end up with the same problem.
We would create row groups like so:

```
100K rows
1 row
```

Then merge them back into a single row group with size `100K+1`,
effectively performing the same rewrite as before.

Instead, for the last row groups in a file, we need a *minimum
threshold* to merge. This is either the `row group size` itself, or 2X
the size of the first row group we are considering. We also always merge
row groups if the total size is `< 2048` (the vector size). This
exponential merging ensures we don't merge on every single insert, while
also ensuring we never have too many row groups.

We can see this process in action when starting with 100K rows, and
inserting 100 rows at a time - effectively repeating the below script:

```sql
insert into z select 'a','b','c' from range(100);
checkpoint;
select row_group_id, max(count) from pragma_storage_info('z') group by all order by all;
```

```sql
 -- insert batch #1
┌──────────────┬────────────┐
│ row_group_id │ max(count) │
│    int64     │   int64    │
├──────────────┼────────────┤
│            0 │     100000 │
│            1 │        100 │
└──────────────┴────────────┘

-- insert batch #30
┌──────────────┬────────────┐
│ row_group_id │ max(count) │
│    int64     │   int64    │
├──────────────┼────────────┤
│            0 │     100000 │
│            1 │       2000 │
│            2 │       1000 │
└──────────────┴────────────┘
-- insert batch duckdb#150
┌──────────────┬────────────┐
│ row_group_id │ max(count) │
│    int64     │   int64    │
├──────────────┼────────────┤
│            0 │     100000 │
│            1 │       8000 │
│            2 │       4000 │
│            3 │       2000 │
│            4 │       1000 │
└──────────────┴────────────┘
-- insert batch duckdb#228
┌──────────────┬────────────┐
│ row_group_id │ max(count) │
│    int64     │   int64    │
├──────────────┼────────────┤
│            0 │     100000 │
│            1 │      16000 │
│            2 │       4000 │
│            3 │       2000 │
│            4 │        800 │
└──────────────┴────────────┘
-- insert batch duckdb#229
┌──────────────┬────────────┐
│ row_group_id │ max(count) │
│    int64     │   int64    │
├──────────────┼────────────┤
│            0 │     122800 │
│            1 │        100 │
└──────────────┴────────────┘
```


### Performance

Running the above example again, the checkpoint now completes in `0.005`
seconds, instead of `0.6` seconds.

Note that we still do the compaction at some point, so while most
checkpoints will have gotten faster, not all of them will have gotten
faster.

Running the above example 300X, here are the timings:

```sql
create table z as select repeat(sha256(i::varchar), 10) as a, repeat(sha256((i**2)::varchar), 10) as b, repeat(sha256((i**3)::varchar), 10) as c from range(100000) r(i);
-- 300X the below insertion
insert into z select 'a','b','c' from range(100);
CHECKPOINT;
```

|           Summary           | v1.3.2  |  New   |
|-----------------------------|---------|--------|
| Total Time                  | 128.82s | 1.00s  |
| Average Time Per Checkpoint | 0.56s   | 0.01s  |
| Max Checkpoint Time         | 0.631s  | 0.526s |

In the above example, there is still a single checkpoint that does the
full on compaction, and thus has the same timing as the original script
had for every checkpoint.