v1.17: quic: use smallvec to aggregate chunks, save 1 alloc per packet (backport of #735)

[mergify]

Use smallvec to hold chunks. Streams are packet-sized so we don't expect them to have many chunks. This saves us an allocation for each packet.

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This is an automatic backport of pull request #735 done by Mergify.

[mergify]

Cherry-pick of 55ab7fa has failed:

On branch mergify/bp/v1.17/pr-735
Your branch is up to date with 'origin/v1.17'.

You are currently cherry-picking commit 55ab7fadbc.
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  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   Cargo.lock
	both modified:   Cargo.toml
	both modified:   programs/sbf/Cargo.lock
	both modified:   streamer/Cargo.toml
	both modified:   streamer/src/nonblocking/quic.rs

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.6%. Comparing base (be83469) to head (0dc42a4).
Report is 2 commits behind head on v1.17.

Additional details and impacted files

@@           Coverage Diff           @@
##            v1.17     #741   +/-   ##
=======================================
  Coverage    81.6%    81.6%           
=======================================
  Files         806      806           
  Lines      219284   219283    -1     
=======================================
+ Hits       179014   179079   +65     
+ Misses      40270    40204   -66     

[steviez]

Missed the pre-merge review, but this looks good to me

[behzadnouri]

Was there any testing done here that this backport to stable branch was necessary?
Like if it moves a needle or not.