[PR #10049/006fbc37 backport][3.11] Improve client performance when there are no auto headers to skip

[patchback]

This is a backport of PR #10049 as merged into master (006fbc3).

Skipping auto headers is a rarely used feature.

• Avoid making an empty CIMultiDict each request that we will throw away
• Avoid all the contains checks when there are no auto headers to skip
• Some unreachable branching has been removed from update_body_from_data

[codspeed-hq]

CodSpeed Performance Report

Merging #10051 will not alter performance

_{Comparing patchback/backports/3.11/006fbc376bf8eac9cbe54a902b09e1975bd1ff41/pr-10049 (85435fb) with 3.11 (d411bc5)}

Summary

✅ 44 untouched benchmarks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.03%. Comparing base (d411bc5) to head (85435fb).
Report is 1 commits behind head on 3.11.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             3.11   #10051   +/-   ##
=======================================
  Coverage   98.03%   98.03%           
=======================================
  Files         122      122           
  Lines       36932    36935    +3     
  Branches     4450     4449    -1     
=======================================
+ Hits        36207    36211    +4     
  Misses        543      543           
+ Partials      182      181    -1     

Flag	Coverage Δ
CI-GHA	97.93% <100.00%> (+<0.01%)	⬆️
OS-Linux	97.63% <100.00%> (+<0.01%)	⬆️
OS-Windows	94.53% <100.00%> (+<0.01%)	⬆️
OS-macOS	96.75% <100.00%> (+0.01%)	⬆️
Py-3.10.11	96.60% <100.00%> (+2.49%)	⬆️
Py-3.10.15	97.14% <100.00%> (+0.67%)	⬆️
Py-3.11.10	97.21% <100.00%> (+<0.01%)	⬆️
Py-3.11.9	96.67% <100.00%> (+2.51%)	⬆️
Py-3.12.7	97.70% <100.00%> (+<0.01%)	⬆️
Py-3.13.0	97.69% <100.00%> (+<0.01%)	⬆️
Py-3.9.13	96.53% <100.00%> (+<0.01%)	⬆️
Py-3.9.20	97.10% <100.00%> (+0.03%)	⬆️
Py-pypy7.3.16	96.67% <100.00%> (-0.01%)	⬇️
VM-macos	96.75% <100.00%> (+0.01%)	⬆️
VM-ubuntu	97.63% <100.00%> (+<0.01%)	⬆️
VM-windows	94.53% <100.00%> (+<0.01%)	⬆️

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