Improve client performance when there are no auto headers to skip

[bdraco]

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.73%. Comparing base (c3c11a6) to head (047ab36).
Report is 1 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #10049   +/-   ##
=======================================
  Coverage   98.73%   98.73%           
=======================================
  Files         121      121           
  Lines       36768    36771    +3     
  Branches     4393     4392    -1     
=======================================
+ Hits        36303    36307    +4     
  Misses        314      314           
+ Partials      151      150    -1     

Flag	Coverage Δ
CI-GHA	98.62% <100.00%> (+<0.01%)	⬆️
OS-Linux	98.31% <100.00%> (+<0.01%)	⬆️
OS-Windows	96.15% <100.00%> (+<0.01%)	⬆️
OS-macOS	97.41% <100.00%> (+<0.01%)	⬆️
Py-3.10.11	97.26% <100.00%> (+<0.01%)	⬆️
Py-3.10.15	97.80% <100.00%> (+<0.01%)	⬆️
Py-3.11.10	97.85% <100.00%> (-0.05%)	⬇️
Py-3.11.9	97.31% <100.00%> (+<0.01%)	⬆️
Py-3.12.7	98.37% <100.00%> (+<0.01%)	⬆️
Py-3.13.0	98.37% <100.00%> (+<0.01%)	⬆️
Py-3.9.13	97.18% <100.00%> (-0.01%)	⬇️
Py-3.9.20	97.76% <100.00%> (+<0.01%)	⬆️
Py-pypy7.3.16	97.33% <100.00%> (+<0.01%)	⬆️
VM-macos	97.41% <100.00%> (+<0.01%)	⬆️
VM-ubuntu	98.31% <100.00%> (+<0.01%)	⬆️
VM-windows	96.15% <100.00%> (+<0.01%)	⬆️

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[codspeed-hq]

CodSpeed Performance Report

Merging #10049 will not alter performance

_{Comparing skip_auto_headers_perf (047ab36) with master (c3c11a6)}

Summary

✅ 44 untouched benchmarks

[patchback]

Backport to 3.11: 💚 backport PR created

✅ Backport PR branch: patchback/backports/3.11/006fbc376bf8eac9cbe54a902b09e1975bd1ff41/pr-10049

Backported as #10051

🤖 @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/3.12/006fbc376bf8eac9cbe54a902b09e1975bd1ff41/pr-10049

Backported as #10052

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