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

docs/reference/settings.md

@@ -127,6 +127,31 @@ default-groups = ["docs"]
 
 ---
 
+### [`dependency-groups`](#dependency-groups) {: #dependency-groups }
+
+Additional settings for `dependency-groups`.
+
+Currently this can only be used to add `requires-python` constraints
+to dependency groups (typically to inform uv that your dev tooling
+has a higher python requirement than your actual project).
+
+This cannot be used to define dependency groups, use the top-level
+`[dependency-groups]` table for that.
+
+**Default value**: `[]`
+
+**Type**: `dict`
+
+**Example usage**:
+
+```toml title="pyproject.toml"
+
+[tool.uv.dependency-groups]
+my-group = {requires-python = ">=3.12"}
+```
+
+---
+
 ### [`dev-dependencies`](#dev-dependencies) {: #dev-dependencies }
 
 The project's development dependencies.