Fix typing of TypeAdapter

[Viicos]

Change Summary

Fixes #9532

Dirty playgrounds if you want to play with it: pyright, mypy.

The only drawback is this is allowed:

ta = TypeAdapter[int](str)

As type checkers will fallback to the second overload. However, the following works as expected:

TypeAdapter(int)  # TypeAdapter[int], no type errors
TypeAdapter[int](int)  # TypeAdapter[int], no type errors
TypeAdapter[str | int](str | int)  # TypeAdapter[str | int], no type errors
TypeAdapter[int](Annotated[int, ...])  # TypeAdapter[int], no type errors

I think the TypeForm PEP is just around the corner, so this is really only a temporary fix until we get something working as expected for all use cases.

Related issue number

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

Selected Reviewer: @davidhewitt

[codspeed-hq]

CodSpeed Performance Report

Merging #9570 will not alter performance

_{Comparing Viicos:type-adapter-typing (edf747c) with main (137d4d8)}

Summary

✅ 13 untouched benchmarks

[Viicos]

Please review

[davidhewitt]

@adriangb will pass this over to you, as it looks like you made the last edits to these points.

I think I agree with the PR here and we should wait for the TypeForm PEP to get perfect behaviour later, however want to let you make the final call.

[adriangb]

Seems like we can't win here right now, we're going to have either false negatives or false positives. And I think the false positives are more annoying, so LGTM.