perf(quinn-proto): Avoid creating small Bytes when doing small writes via AsyncWrite::write

[rklaehn]

Description

Defers the creation of the Bytes a tiny bit more, so we can decide in the SendBufferData to either copy or create a Bytes.

For anything less than MAX_COMBINE, we will not create a Bytes at all.

Breaking Changes

None

Notes & open questions

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.80%. Comparing base (695025c) to head (a81ead9).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #252      +/-   ##
==========================================
+ Coverage   76.78%   76.80%   +0.02%     
==========================================
  Files          83       83              
  Lines       23473    23497      +24     
==========================================
+ Hits        18023    18047      +24     
  Misses       5450     5450              

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[github-actions]

Documentation for this PR has been generated and is available at: https://n0-computer.github.io/quinn/pr/252/docs/iroh_quinn/

Last updated: 2025-12-23T14:05:47Z