[proxy] use the proxy protocol v2 command to silence some logs

[conradludgate]

The PROXY Protocol V2 offers a "command" concept. It can be of two different values. "Local" and "Proxy". The spec suggests that "Local" be used for health-checks. We can thus use this to silence logging for such health checks such as those from NLB.

This additionally refactors the flow to be a bit more type-safe, self documenting and using zerocopy deser.

[github-actions]

5328 tests run: 5106 passed, 0 failed, 222 skipped (full report)

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Flaky tests (1)

Postgres 17

• test_sharding_split_smoke: debug-x86-64

Code coverage* (full report)

• functions: 31.5% (7797 of 24752 functions)
• lines: 48.9% (61135 of 124940 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
345f9e7 at 2024-11-04T18:17:29.453Z :recycle:}