Apply ruff/flake8-pyi preview rule PYI059

[DimitriPapadopoulos]

PYI059 Generic[] should always be the last base class

If Generic[] is not the final class in the bases tuple, unexpected behaviour can occur at runtime (See this CPython issue for an example).

TODO:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in docs/user-guide/*.rst
• Changes documented as a new file in changes/
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)