…`MnNetInfo`, lay some groundwork for managing multiple entries

1d52678 refactor: track every `MnNetInfo` entry in the unique property map (Kittywhiskers Van Gogh)
bcb8a7d refactor: impl `GetEntries()`, adapt to support multiple addresses (Kittywhiskers Van Gogh)
ecc9368 refactor: implement `MnNetInfo::ToString()` for printing internal state (Kittywhiskers Van Gogh)
2e9bde0 refactor: move service validation to `MnNetInfo`, run during setting (Kittywhiskers Van Gogh)
03ec604 fix: correct `simplifiedmns_merkleroots` unit test (Kittywhiskers Van Gogh)
bac4a27 refactor: move address lookup to `MnNetInfo::AddEntry()` (Kittywhiskers Van Gogh)
e1783cb refactor: remove direct access to `MnNetInfo::addr` (Kittywhiskers Van Gogh)
e868aff refactor: use const-ref when accessing `MnNetInfo::addr` if read-only (Kittywhiskers Van Gogh)
aaabc35 refactor: section off masternode service to `MnNetInfo` (Kittywhiskers Van Gogh)
2c6dd05 fix: avoid potential "no user-provided default constructor" error (Kittywhiskers Van Gogh)

Pull request description:

  ## Additional Information

  * Depends on #6626

  * Depends on #6635

  * Depends on #6636

  * Dependency for #6629

  * The `simplifiedmns_merkleroots` test constructs 15 `CSimplifiedMNListEntry` elements and populates them with a `CService`. So far, since we allowed direct assignment of the `CService` without validation, no checks were made to see if they would pass validation but if we start enforcing validation rules _when setting values_, two problems emerge.

    * Using non-default ports on mainnet (`BasicTestingSetup` is mainnet by default, [source](https://github.com/dashpay/dash/blob/bcd14b05cec7d94986f114ca17bbdadbee701d9b/src/test/util/setup_common.h#L100)), this has been resolved by using `RegTestingSetup` (which is based on regtest) instead.

    * As the index is used to generate the address, starting from 0, the first address is `0.0.0.0`, which is not a valid `CService` address ([source](https://github.com/dashpay/dash/blob/bcd14b05cec7d94986f114ca17bbdadbee701d9b/src/test/net_tests.cpp#L140)) and therefore, would fail validation ([source](https://github.com/dashpay/dash/blob/bcd14b05cec7d94986f114ca17bbdadbee701d9b/src/evo/deterministicmns.cpp#L1219)). This has been resolved by changing the index to start from 1.

  * To avoid a potential "no user-provided default constructor" compile-time error, we now explicitly request the default constructor

    <details>

    <summary>Compile error:</summary>

    ```
    In file included from evo/deterministicmns.cpp:5:
    ./evo/deterministicmns.h:404:24: error: default initialization of an object of const type 'const ExampleType' without a user-provided default constructor
      404 |         static const T nullValue;
          |                        ^
          |                                 {}
    evo/deterministicmns.cpp:479:18: note: in instantiation of function template specialization 'CDeterministicMNList::AddUniqueProperty<ExampleType>' requested here
      479 |             if (!AddUniqueProperty(*dmn, domain)) {
          |                  ^
    ```

   </details>

  * The reason why we track individual entries _within_ `MnNetInfo` in the unique properties map instead of `MnNetInfo` is that while `MnNetInfo`-like objects (because `MnNetInfo` itself only stores one value) could check _internally_ for duplicates, the uniqueness requirement for addresses is _across_ ProTx'es and therefore, we are concerned not so much as _how_ the addresses are bundled (`MnNetInfo`) but if the individual addresses (`CService`) are unique _across_ all known addresses.

  * We cannot use `const auto&` when iterating through `GetEntries()` as it uses `std::reference_wrapper<const T>` and `auto` will take on the type of `const std::reference_wrapper<const T>&` instead of the underlying `const T&` as intended, to trigger the conversion to the underlying reference, we have to explicitly specify the type, hence the usage of `const T&`.

  ## Breaking Changes

  None expected.

  ## Checklist

  - [x] I have performed a self-review of my own code
  - [x] I have commented my code, particularly in hard-to-understand areas
  - [x] I have added or updated relevant unit/integration/functional/e2e tests
  - [x] I have made corresponding changes to the documentation **(note: N/A)**
  - [x] I have assigned this pull request to a milestone _(for repository code-owners and collaborators only)_

ACKs for top commit:
  knst:
    utACK 1d52678
  UdjinM6:
    utACK 1d52678

Tree-SHA512: 0f13f51fff6c279e8c4e3f88ea4db925f4137e25b030d28afd48b5db9c073421d5bb3a3dc3e067ee4f559887bec9e8a981d2e6ae5f2d0a042e5817a3d59ea0bf