[DONTMERGE] Test run with reproducer for forced chunked send #36724

WARNING: NOT INTENDED FOR MERGING!

Performing a test run with forced chunked send.

All networking code using sockets must not make assumption about the chunking of the incoming/outgoing data, and should be resilient against any chunking. Normally, the chunking of the sends of the writer dictate the chunking of the receives at the reader, but this is not guaranteed by IP/TCP, intermediate networking elements may change the packet structure.

This branch contains a stress test reproducer. For every socket send, sending is changed to break up data in small chunks. This forcedly changes chunking of the data stream. The goal is to test code for robustness in face of unexpected chunking of the data.

This PR will be closed once the test runs complete, and kept for reference (some tests are expected to fail).

WARNING: NOT INTENDED FOR MERGING!

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The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

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External sites

• Code coverage & benchmarks: https://corecheck.dev/bitcoin/bitcoin/pulls/36724
• Ralph review <img src=https://review.fish.foo/assets/bitcoin/bitcoin/36724.png alt="Ralph review status"> https://git.fish.foo/bitcoin/bitcoin/pulls/36724#author-ralph

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Reviews

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🚧 At least one of the CI tasks failed. _{Task iwyu: https://github.com/bitcoin/bitcoin/actions/runs/41417100283/job/125183540072} _{LLM reason (✨ experimental): CI failed because IWYU required adding <thread> to src/util/sock.cpp, leaving a diff that the include-check rejects.}

<details><summary>Hints</summary>

Try to run the tests locally, according to the documentation. However, a CI failure may still happen due to a number of reasons, for example:

• Possibly due to a silent merge conflict (the changes in this pull request being incompatible with the current code in the target branch). If so, make sure to rebase on the latest commit of the target branch.

• A sanitizer issue, which can only be found by compiling with the sanitizer and running the affected test.

• An intermittent issue.

Leave a comment here, if you need help tracking down a confusing failure.

</details>

CI runs have completed, with some failures. An issue has been raised to document the failed tests -- #36726 . Closing this PR (was not intended for merging, kept for reference).