Add benchmark for field validator functions

[adriangb]

Selected Reviewer: @samuelcolvin

[adriangb]

please review

[codecov]

Codecov Report

Merging #726 (9eef7c7) into main (0d12efd) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #726   +/-   ##
=======================================
  Coverage   93.63%   93.63%           
=======================================
  Files          99       99           
  Lines       13911    13911           
  Branches       25       25           
=======================================
  Hits        13026    13026           
  Misses        879      879           
  Partials        6        6           

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[codspeed-hq]

CodSpeed Performance Report

Merging #726 will not alter performances

_{Comparing field-validator-bench (9eef7c7) with main (0d12efd)}

Summary

✅ 125 untouched benchmarks

🆕 1 new benchmarks

Benchmarks breakdown

	Benchmark	main	field-validator-bench	Change
🆕	test_field_function_validator	N/A	941.3 µs	N/A