… fuzz test coverage

e337145 [fuzz] Occasional valid magic bytes for transport serialization test (Dhruv Mehta)
35571d8 [fuzz] Occasional valid checksum for transport serialization fuzz test (Dhruv Mehta)
654472a [fuzz] Add serialization to deserialization test (Dhruv Mehta)

Pull request description:

  This PR has 3 commits that increase the fuzz test coverage:

  Before commit 1:
  ```
  #306853 REDUCE cov: 798 ft: 5820 corp: 150/375Kb lim: 68333 exec/s: 1382 rss: 461Mb L: 254/63171 MS: 1 EraseBytes-
  #1453105 REDUCE cov: 798 ft: 5820 corp: 150/369Kb lim: 79613 exec/s: 1467 rss: 461Mb L: 6027/60873 MS: 1 EraseBytes-
  ```

  After commit 1 (adds serialization to de-serialization test):
  ```
  #303389 NEW cov: 1202 ft: 8382 corp: 157/382Kb lim: 68189 exec/s: 1451 rss: 447Mb L: 1386/65459 MS: 1 CopyPart-
  #1428759 REDUCE cov: 1202 ft: 8512 corp: 169/389Kb lim: 78749 exec/s: 1528 rss: 463Mb L: 1627/60488 MS: 1 EraseBytes-
  ```

  After commit 2 (provides an occasional checksum assist to the fuzzer inputs):
  ```
  #304820 NEW cov: 1440 ft: 4452 corp: 92/12551b lim: 2237 exec/s: 3386 rss: 486Mb L: 47/1111 MS: 1 ChangeByte-
  #1416181 REDUCE cov: 1442 ft: 5681 corp: 125/59Kb lim: 4096 exec/s: 3522 rss: 535Mb L: 2164/4049 MS: 1 EraseBytes-
  ```

  After commit 3 (provides an occasional magic bytes assist to the fuzzer inputs):
  ```
  #302684 NEW cov: 1454 ft: 3936 corp: 84/7056b lim: 2424 exec/s: 4146 rss: 477Mb L: 65/1108 MS: 3 CopyPart-CrossOver-CMP- DE: "\x0e\x00\x00\x00"-
  #1383925 REDUCE cov: 1454 ft: 4828 corp: 102/14573b lim: 4096 exec/s: 3954 rss: 534Mb L: 116/4050 MS: 2 EraseBytes-ChangeByte-
  ```

  If reviewers only accept the first commit, the seeds are not invalidated and new seeds are at: bitcoin-core/qa-assets#61. In this case, we can also revert the test name change.

  If reviewers accept all three commits, the existing seeds are invalidated.

ACKs for top commit:
  practicalswift:
    Tested ACK e337145

Tree-SHA512: d37f06eea0249322b00a99c4827359eb53aeb711751e5571f4681eeca06dc257e0c4cd4887150fc37cc2f689e26986112d768066ad274361615ba9b6a522c61a

…st coverage

e337145 [fuzz] Occasional valid magic bytes for transport serialization test (Dhruv Mehta)
35571d8 [fuzz] Occasional valid checksum for transport serialization fuzz test (Dhruv Mehta)
654472a [fuzz] Add serialization to deserialization test (Dhruv Mehta)

Pull request description:

  This PR has 3 commits that increase the fuzz test coverage:

  Before commit 1:
  ```
  #306853 REDUCE cov: 798 ft: 5820 corp: 150/375Kb lim: 68333 exec/s: 1382 rss: 461Mb L: 254/63171 MS: 1 EraseBytes-
  #1453105 REDUCE cov: 798 ft: 5820 corp: 150/369Kb lim: 79613 exec/s: 1467 rss: 461Mb L: 6027/60873 MS: 1 EraseBytes-
  ```

  After commit 1 (adds serialization to de-serialization test):
  ```
  #303389 NEW cov: 1202 ft: 8382 corp: 157/382Kb lim: 68189 exec/s: 1451 rss: 447Mb L: 1386/65459 MS: 1 CopyPart-
  #1428759 REDUCE cov: 1202 ft: 8512 corp: 169/389Kb lim: 78749 exec/s: 1528 rss: 463Mb L: 1627/60488 MS: 1 EraseBytes-
  ```

  After commit 2 (provides an occasional checksum assist to the fuzzer inputs):
  ```
  #304820 NEW cov: 1440 ft: 4452 corp: 92/12551b lim: 2237 exec/s: 3386 rss: 486Mb L: 47/1111 MS: 1 ChangeByte-
  #1416181 REDUCE cov: 1442 ft: 5681 corp: 125/59Kb lim: 4096 exec/s: 3522 rss: 535Mb L: 2164/4049 MS: 1 EraseBytes-
  ```

  After commit 3 (provides an occasional magic bytes assist to the fuzzer inputs):
  ```
  #302684 NEW cov: 1454 ft: 3936 corp: 84/7056b lim: 2424 exec/s: 4146 rss: 477Mb L: 65/1108 MS: 3 CopyPart-CrossOver-CMP- DE: "\x0e\x00\x00\x00"-
  #1383925 REDUCE cov: 1454 ft: 4828 corp: 102/14573b lim: 4096 exec/s: 3954 rss: 534Mb L: 116/4050 MS: 2 EraseBytes-ChangeByte-
  ```

  If reviewers only accept the first commit, the seeds are not invalidated and new seeds are at: bitcoin-core/qa-assets#61. In this case, we can also revert the test name change.

  If reviewers accept all three commits, the existing seeds are invalidated.

ACKs for top commit:
  practicalswift:
    Tested ACK e337145

Tree-SHA512: d37f06eea0249322b00a99c4827359eb53aeb711751e5571f4681eeca06dc257e0c4cd4887150fc37cc2f689e26986112d768066ad274361615ba9b6a522c61a