Avoid calling len on the same data in the stream reader twice

[bdraco]

This is trivial but it is noticeable in the profile.

before

after

[bdraco]

I only found this because I was looking at function call counts..

I was trying to find why _release_connection is always called 4x per request

[codspeed-hq]

CodSpeed Performance Report

Merging #10088 will not alter performance

_{Comparing dupe_len_call_read_nowait_chunk (3ad907e) with master (ca193c7)}

Summary

✅ 44 untouched benchmarks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.76%. Comparing base (ca193c7) to head (3ad907e).
Report is 1 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #10088   +/-   ##
=======================================
  Coverage   98.76%   98.76%           
=======================================
  Files         121      121           
  Lines       36866    36867    +1     
  Branches     4396     4396           
=======================================
+ Hits        36409    36410    +1     
  Misses        311      311           
  Partials      146      146           

Flag	Coverage Δ
CI-GHA	98.64% <100.00%> (+<0.01%)	⬆️
OS-Linux	98.33% <100.00%> (+<0.01%)	⬆️
OS-Windows	96.18% <100.00%> (+<0.01%)	⬆️
OS-macOS	97.43% <100.00%> (-0.01%)	⬇️
Py-3.10.11	97.28% <100.00%> (-0.01%)	⬇️
Py-3.10.15	97.88% <100.00%> (+<0.01%)	⬆️
Py-3.11.10	97.86% <100.00%> (-0.01%)	⬇️
Py-3.11.9	97.33% <100.00%> (-0.02%)	⬇️
Py-3.12.7	98.39% <100.00%> (+<0.01%)	⬆️
Py-3.13.0	98.39% <100.00%> (+<0.01%)	⬆️
Py-3.9.13	97.21% <100.00%> (+<0.01%)	⬆️
Py-3.9.20	97.79% <100.00%> (+<0.01%)	⬆️
Py-pypy7.3.16	97.35% <100.00%> (-0.01%)	⬇️
VM-macos	97.43% <100.00%> (-0.01%)	⬇️
VM-ubuntu	98.33% <100.00%> (+<0.01%)	⬆️
VM-windows	96.18% <100.00%> (+<0.01%)	⬆️

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[patchback]

Backport to 3.11: 💚 backport PR created

✅ Backport PR branch: patchback/backports/3.11/29c3ca93a4d1793c60d33038151228962f8b6f78/pr-10088

Backported as #10090

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

[patchback]

Backport to 3.12: 💚 backport PR created

✅ Backport PR branch: patchback/backports/3.12/29c3ca93a4d1793c60d33038151228962f8b6f78/pr-10088

Backported as #10091

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