proxy: report blame for passthrough disconnect io errors

[conradludgate]

Problem

Hard to debug the disconnection reason currently.

Summary of changes

Keep track of error-direction, and therefore error source (client vs compute) during passthrough.

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]

2910 tests run: 2793 passed, 0 failed, 117 skipped (full report)

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Code coverage* (full report)

• functions: 32.8% (6894 of 21018 functions)
• lines: 50.3% (53909 of 107202 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
d0feece at 2024-06-26T15:25:17.551Z :recycle:}

[khanova]

Looks very good!