Use dependency groups (PEP 735) - #15366

This PR moves some dependency lists from project.optional-dependencies (aka "extras") to dependency-groups, as described by PEP 735. Some details:

• Keep black, matplotlib and all as "extras" intended for end-users
• Move docs (renamed from doc), test, and test_extra to dependency groups, intended for developers
  • Note that pip install --dryrun ipython[test] will show a warning that the package does not have an extra named test.
  • Developers that need this dependency will require pip v25.1 (2025-04-26) (or uv) and use the --group test option
• Add a build group with tools needed to build this package
• Add a dev group, which adds pre-commit and the build and test groups; uv enables this group by default.
• Merge docs/requirements.txt into the docs group, and remove this file, as it is unnecessary duplication
• Rewrite a few "uv pip install" commands into one line, as it often works best to solve a larger group of dependencies at once