add build-pgo make target

[davidhewitt]

Change Summary

Adds make build-pgo target, as requested in #678 (comment)

Related issue number

N/A

Checklist

• Unit tests for the changes exist
• Documentation reflects the changes where applicable
• Pydantic tests pass with this pydantic-core (except for expected changes)
• My PR is ready to review, please add a comment including the phrase "please review" to assign reviewers

Selected Reviewer: @samuelcolvin

[davidhewitt]

please review

[codecov]

Codecov Report

Merging #741 (6b357d3) into main (d08d269) will increase coverage by 0.01%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #741      +/-   ##
==========================================
+ Coverage   93.63%   93.64%   +0.01%     
==========================================
  Files          99       99              
  Lines       13895    13929      +34     
  Branches       25       25              
==========================================
+ Hits        13010    13044      +34     
  Misses        879      879              
  Partials        6        6              

see 7 files with indirect coverage changes

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[codspeed-hq]

CodSpeed Performance Report

Merging #741 will not alter performances

_{Comparing dh/make-pgo (6b357d3) with main (d08d269)}

Summary

✅ 126 untouched benchmarks

[davidhewitt]

I pushed another commit which switches automatically to use maturin if the conditions look suitable (a virtualenv is active and maturin is installed), @adriangb confirmed on slack this is working so I'll merge now.