Add `[tool.uv.dependency-groups].mygroup.requires-python` (#13735)
This allows you to specify requires-python on individual dependency-groups,
with the intended usecase being "oh my dev-dependencies have a higher
requires-python than my actual project".
This includes a large driveby move of the RequiresPython type to
uv-distribution-types to allow us to generate the appropriate markers at
this point in the code. It also migrates RequiresPython from
pubgrub::Range to version_ranges::Ranges, and makes several pub(crate)
items pub, as it's no longer defined in uv_resolver.
Fixes #11606
