feat(pep621): add support for dependency-groups (PEP 735)

[mkniewallner]

Closes #32147.

Changes

Add support for Python dependency-groups, which recently got accepted as part of PEP 735.

Context

As mentioned in the linked discussion, not all tools that support PEP 621 for defining project dependencies support dependency-groups (so far, only uv does AFAIK), but since the feature would only be used by users of tools that support it, it should not be problematic to assume that all tools support it already.

But if you feel like we should take a more defensive approach and only parse dependencies for tools that explicitly support it, happy to update the PR.

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

Tested over https://github.com/mkniewallner/renovate-uv-dependency-groups.