Add support for Python dependency-groups (PEP 735)

[mkniewallner]

Tell us more.

PEP 735 recently got accepted. Similarly to optional-dependencies or tool.pdm.dev-dependencies, it allows defining groups of dependencies in pyproject.toml like so:

[dependency-groups]
test = ["pytest==8.3.3", "pytest-cov==5.0.0"]
typing = ["mypy==1.13.0"]
all = [{include-group = "test"}, {include-group = "typing"}, "click"]

When a dependency in a group is not a string, but instead a table, we should skip parsing it, as the only key is include-group, which is not relevant for Renovate itself (it only allows reusing a group in another group).

Not all tools that support PEP 621 support dependency-groups yet (so far, only uv supports it, AFAIK), but I don't think it would be too problematic to already assume that all tools support it, as if a user uses a dependency manager that does not yet support dependency-groups, they would have no reason to use the feature anyway.

Would be happy to work on the implementation.

[mkniewallner]

Resolved by #32148.