- Remove now-removed configuration values
- Use obvious 'unset' defaults for ``project`` and ``author``
- Prefer 'e.g.' to 'ex.'
- Allow non-list sequence types in various configuration values
- Add types and defaults to every confval directive
Add `tests/test_theming/test_theming.py::test_theme_builds`, which is a parametrized test against all builtin sphinx HTML themes, that tests:
1. that the themes builds without warnings for a basic project, and
2. that all `.html` files it produces are valid XML (see https://html.spec.whatwg.org/)
https://pypi.org/project/defusedxml/ was added to the test dependencies, in order to safely parse the XML
This required one fix for `sphinx/themes/basic/search.html`, and one for `sphinx/themes/bizstyle/layout.html`
Also, `tests/test_theming` was removed from the `ruff format` exclude list
