reduce complexity of proxy protocol parse

[conradludgate]

Problem

The WithClientIp AsyncRead/Write abstraction never filled me with much joy. I would just rather read the protocol header once and then get the remaining buf and reader.

Summary of changes

• Replace WithClientIp::wait_for_addr with read_proxy_protocol.
• Replace WithClientIp with ChainRW.
• Optimise ChainRW to make the standard path more optimal.

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

2772 tests run: 2654 passed, 0 failed, 118 skipped (full report)

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Flaky tests (1)

Postgres 16

• test_compute_pageserver_connection_stress: release

Code coverage* (full report)

• functions: 28.1% (6461 of 23024 functions)
• lines: 46.8% (45616 of 97518 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
0d0fba1 at 2024-04-22T15:36:26.877Z :recycle:}