Move the current Sphinx docs for the python API to mkdocs

[rachelcarpenterseequent]

All of the documentation in this repo uses mkdocs, apart from the python documentation which has it's own build process and toolchain.

To make things easier, move the python documentation toolchain to be mkdocs.
Using the plugin mkdocstrings which builds basic documentation for modules from docstrings. This matches the functionality of the previous Sphinx autogenerated documentation. https://mkdocstrings.github.io/

No new documentation added. Tested by building locally, using the same bash script that the GitHub action uses. The GitHub action will continue to fail unless we enable GitHub pages for this forked repo, but should work in the upstream repo where this is enabled.

Screenshot of docs:

[Tim-Evans-Seequent]

@rachelcarpenterseequent I've pushed a few changes:

• Merged the upgrade rust branch into this one to avoid conflicts.
• Fixed the doc build scripts, as they didn't work on a clean checkout.
• Added a top-of-crate doc-comment to the omf_python crate, and include it in the generated stub file.
• With the top-of-crate doc-comment providing the introduction now, I have merged the two pages of Python docs.

The remaining problem is larger: these extracted Python doc-strings look terrible. The formatting makes them basically impossible to use. My guess is that mkdocstrings-python is expecting certain CSS classes that aren't present in the rest of the docs.

The scrolling of the contents list on the left is also wrong. You can't read the whole thing until you scroll right to the bottom of that rather large page. That could be fixed by breaking things up into multiple pages maybe.

If there's no easy way to fix that then I would prefer Python worked the same was as Rust, and we generate the docs separately and just link to them.

[robbieaverill]

LGTM. There will be some conflicts and overlap with #41 though, so it might be worth merging that before this one.

[Tim-Evans-Seequent]

Will land this now, as it solves some issues. We can address the formatting in another PR