added @classmethod to @model_validator(mode='before') in docs and acr…

[paulmartin91]

…oss app

Change Summary

• For clarity/consistency, added the @classmethod decorator to methods with @model_validate(mode="before"), as described in the docs.

"Before model validators should be class methods. The first argument should be cls (and we also recommend you use @classmethod below @model_validator for proper type checking),"

https://docs.pydantic.dev/latest/concepts/validators/#model-validators

Related issue number

#9407

Checklist

• [ x] The pull request title is a good summary of the changes - it will be used in the changelog
• [ x] Unit tests for the changes exist
• [ x] Tests pass on CI
• [ x] Documentation reflects the changes where applicable
• [ x] My PR is ready to review, please add a comment including the phrase "please review" to assign reviewers

Selected Reviewer: @davidhewitt

[paulmartin91]

please review

[codspeed-hq]

CodSpeed Performance Report

Merging #9410 will not alter performance

_{Comparing paulmartin91:model-validator-classmethods (a9697ab) with main (07b6473)}

Summary

✅ 13 untouched benchmarks