perf/bench: remove unnecessary heap allocs in asio accept_churn benches

[mvandeberg]

Replace unique_ptr<tcp_socket> with value-typed sockets across all asio accept_churn benchmarks (coroutine and callback variants). Vectors are pre-reserved so no reallocation invalidates references held by pending async operations. This matches the corosio benchmark's allocation pattern for an apples-to-apples comparison.

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[cppalliance-bot]

An automated preview of the documentation is available at https://237.corosio.prtest3.cppalliance.org/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2026-04-21 21:47:33 UTC

[cppalliance-bot]

GCOVR code coverage report https://237.corosio.prtest3.cppalliance.org/gcovr/index.html
LCOV code coverage report https://237.corosio.prtest3.cppalliance.org/genhtml/index.html
Coverage Diff Report https://237.corosio.prtest3.cppalliance.org/diff-report/index.html

Build time: 2026-04-21 21:57:59 UTC

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.71%. Comparing base (e49d180) to head (584784e).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #237   +/-   ##
========================================
  Coverage    77.71%   77.71%           
========================================
  Files           96       96           
  Lines         7298     7298           
  Branches      1787     1787           
========================================
  Hits          5672     5672           
  Misses        1108     1108           
  Partials       518      518           

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