Move tool.uv.dev-dependencies (deprecated) to dependency-groups.dev

[janniklasrose]

Summary

• Move python/codegen/pyproject.toml off the deprecated [tool.uv] dev-dependencies key onto the PEP 735 [dependency-groups] dev table.
• See https://docs.astral.sh/uv/concepts/projects/dependencies/#legacy-dev-dependencies for the upstream deprecation note.
• uv.lock does not need regeneration: uv represents both forms with the same [package.dev-dependencies] / [package.metadata.requires-dev] structure.

Test plan

• uv lock --check in python/codegen/ passes (lockfile still consistent with pyproject.toml).

This pull request and its description were written by Isaac.

[github-actions]

Waiting for approval

Based on git history, these people are best suited to review:

• @kanterov -- recent work in python/codegen/

Eligible reviewers: @andrewnester, @anton-107, @denik, @pietern, @renaudhartert-db, @shreyas-goenka, @simonfaltum

_{Suggestions based on git history. See OWNERS for ownership rules.}