Add validate_core_schema function and remove validation from SchemaValidator and SchemaSerializer constructors

[davidhewitt]

Change Summary

Related to startup performance. The idea is that pydantic will have more control over when the CoreSchema gets validated, e.g. validating it once for both SchemaValidator and SchemaSerializer, deciding not to validate it at all based on an env var, etc.

Selected Reviewer: @samuelcolvin

[davidhewitt]

please review

[codecov]

Codecov Report

Merging #982 (d235d90) into main (4c84ed8) will increase coverage by 0.00%.
Report is 1 commits behind head on main.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #982   +/-   ##
=======================================
  Coverage   93.09%   93.09%           
=======================================
  Files         106      106           
  Lines       15830    15832    +2     
  Branches       26       26           
=======================================
+ Hits        14737    14739    +2     
  Misses       1086     1086           
  Partials        7        7           

Files Changed	Coverage Δ
python/pydantic_core/__init__.py	92.59% <ø> (ø)
src/validators/string.rs	98.29% <ø> (ø)
src/lib.rs	100.00% <100.00%> (ø)
src/serializers/mod.rs	98.49% <100.00%> (-0.02%)	⬇️
src/validators/mod.rs	95.23% <100.00%> (+0.03%)	⬆️

... and 1 file with indirect coverage changes

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[codspeed-hq]

CodSpeed Performance Report

Merging #982 will degrade performances by 20.54%

_{Comparing dh/build-both (d235d90) with main (33a7cc0)}

Summary

⚡ 2 improvements
❌ 1 regressions
✅ 135 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	dh/build-both	Change
❌	test_decimal_from_string_core	55.4 µs	69.7 µs	-20.54%
⚡	test_core_model_py	67.1 µs	58.2 µs	+15.41%
⚡	test_model_exclude_unset_false	73.4 µs	63.7 µs	+15.3%

[adriangb]

I'd prefer a method that validates the self-schema, and then remove that from the SchemaValidator and SchemaSerialzier constructors.

[adriangb]

Made the change proposed above. It's also now clear where in our tests we're passing in schemas that need to be coerced, I'd suggest we minimize that and eventually remove it in followup PRs. Ideally a CoreSchema doesn't need to be validated at all.

[davidhewitt]

LGTM, I am author so cannot approve. Feel free to approve & merge.

[davidhewitt]

Might be nice to add a strict flag to make this easier later ;)