proxy: reduce some per-task memory usage

[conradludgate]

Problem

Some tasks are using around upwards of 10KB of memory at all times, sometimes having buffers that swing them up to 30MB.

Summary of changes

Split some of the async tasks in selective places and box them as appropriate to try and reduce the constant memory usage. Especially in the locations where the large future is only a small part of the total runtime of the task.

Also, reduces the size of the CopyBuffer buffer size from 8KB to 1KB.

In my local testing and in staging this had a minor improvement. sadly not the improvement I was hoping for :/ Might have more impact in production

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]

3222 tests run: 3105 passed, 0 failed, 117 skipped (full report)

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Code coverage* (full report)

• functions: 32.4% (6831 of 21071 functions)
• lines: 49.9% (53213 of 106642 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
405df23 at 2024-06-18T17:05:41.766Z :recycle:}