Add docs generation.

[tychedelia]

The docs are generated from the .pyi stubs that generate_stubs already produces. mkdocstrings reads them via griffe's static analysis to build the docs. Apparently this is best practice, there's no single rustdocs equivalent.

A couple things worth noting:

• I had to set module.incomplete = false in generate_stubs because pyo3-introspection marks the module incomplete due to some python things I'm not sure about.
• allow_inspection: false tells giraffe to use the .pyi files.
• show_if_no_docstring: true is needed because the stubs don't have docstrings yet
• We should, in theory, be able to deploy this to github pages for now, which is what the CI sets up.