Drop the mock protocol from the multipart benchmarks

[bdraco]

What do these changes do?

The multipart benchmarks built their StreamReader on a mock.Mock protocol, so every chunk read went through a mock resume_reading() call; that was about a third of the measured time and it is sensitive to the runner environment, which showed up as a spurious 10% regression on #13514. Use a BaseProtocol subclass with no-op flow control instead, as the websocket benchmarks already do.

Are there changes in behavior for the user?

No, benchmarks only.

Is it a substantial burden for the maintainers to support this?

No.

Related issue number

Follow up to #13509, noise seen on #13514.

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes N/A
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    • .misc: Changes that are hard to assign to any of the above
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    Fixed issue with non-ascii contents in doctest text files
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Drafted with Claude Fable 5; reviewed by @bdraco.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.02%. Comparing base (2d9c5c1) to head (8b209ee).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #13515   +/-   ##
=======================================
  Coverage   99.02%   99.02%           
=======================================
  Files         133      133           
  Lines       49924    49927    +3     
  Branches     2594     2594           
=======================================
+ Hits        49439    49442    +3     
  Misses        366      366           
  Partials      119      119           

Flag	Coverage Δ
Autobahn	22.00% <80.00%> (+<0.01%)	⬆️
CI-GHA	98.93% <100.00%> (+<0.01%)	⬆️
OS-Linux	98.70% <100.00%> (+<0.01%)	⬆️
OS-Windows	97.04% <100.00%> (+<0.01%)	⬆️
OS-macOS	97.96% <100.00%> (-0.01%)	⬇️
Py-3.10	98.15% <100.00%> (+<0.01%)	⬆️
Py-3.11	98.39% <100.00%> (-0.01%)	⬇️
Py-3.12	98.47% <100.00%> (-0.01%)	⬇️
Py-3.13	98.46% <100.00%> (+<0.01%)	⬆️
Py-3.14	98.48% <100.00%> (+<0.01%)	⬆️
Py-3.14t	97.58% <100.00%> (+<0.01%)	⬆️
Py-pypy-3.11	97.43% <100.00%> (-0.01%)	⬇️
VM-macos	97.96% <100.00%> (-0.01%)	⬇️
VM-ubuntu	98.70% <100.00%> (+<0.01%)	⬆️
VM-windows	97.04% <100.00%> (+<0.01%)	⬆️
cython-coverage	83.02% <ø> (ø)

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[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge because the benchmark protocol stub supports all flow-control interactions reached by these pre-buffered streams.

The change is confined to benchmark setup, and the replacement protocol provides the connected state and pause/resume methods used by StreamReader without altering user-facing multipart behavior.

_{Reviews (1): Last reviewed commit: "Drop the mock protocol from the multipar..." | Re-trigger Greptile}

[codspeed-hq]

Merging this PR will improve performance by 18.63%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 2 improved benchmarks
✅ 84 untouched benchmarks
⏩ 83 skipped benchmarks¹

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	test_read_base64_part	18.5 ms	15.5 ms	+19.23%
⚡	test_read_chunk_base64_realignment	7.5 ms	6.4 ms	+18.04%

Tip

Curious why this is faster? Comment @codspeedbot explain why this is faster on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing multipart-bench-protocol (8b209ee) with master (2d9c5c1)}

Footnotes

1. 83 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[patchback]

Backport to 3.15: 💚 backport PR created

✅ Backport PR branch: patchback/backports/3.15/495e778360d1924da63e16dba0f0d76baf56a56a/pr-13515

Backported as #13518

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback]

Backport to 3.14: 💚 backport PR created

✅ Backport PR branch: patchback/backports/3.14/495e778360d1924da63e16dba0f0d76baf56a56a/pr-13515

Backported as #13519

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.