Docs update and warning frozen defined both

[mochi22]

Change Summary

This PR addresses an issue where defining frozen both in the @dataclass decorator and config=ConfigDict(frozen=True) led to confusing and inconsistent behavior.
The changes made in this PR aim to clarify the expected behavior and provide better guidance to users.

• docs change

    It's not recommended to define both `frozen` in the `dataclass` decorator and `ConfigDict`.
    If both are defined, the setting from the dataclass decorator will take priority.

In the dataclasses.md file, there was no specific explanation about frozen, so I added an explanation about the frozen setting in ConfigDict(config.py).

• code change

            # It's not recommended to define both, as the setting from the dataclass decorator will take priority.
            if config_wrapper.frozen:
                warn(
                    "Both 'dataclass' decorator and 'config.frozen' are defined. 'config.frozen' take priority.",
                    UserWarning,
                )

Related issue number

fix #9850

Checklist

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

please review: @sydney-runkle

[mochi22]

Hi @sydney-runkle,
Could you please check the PR when it'll be possible!

[codspeed-hq]

CodSpeed Performance Report

Merging #10082 will not alter performance

_{Comparing mochi22:mochi22-issue9850 (f6b2763) with main (cb3ac5a)}

Summary

✅ 17 untouched benchmarks

[sydney-runkle]

Looks like a good start. We've left a few requests for changes. Thanks for your contribution!

[Viicos]

I believe a small test (with pytest.warns) would be great. We also need to specify the correct stacklevel argument, as per my comment.

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
pydantic
dataclasses.py					235
Project Total

This report was generated by python-coverage-comment-action

[sydney-runkle]

Requested 2 other changes. Looks good otherwise, thanks!

[sydney-runkle]

As @Viicos mentioned, I'd love to see a test (and the stacklevel specification)

[sydney-runkle]

@mochi22,

Looks great - can merge once we add a test. Thanks!

[sydney-runkle]

I'll go ahead and merge this and add a test in a separate PR

approved ✅