Doctest fails

[danielward27]

Sphinx doctest fails for a couple reasons. When running doctest

1. Sphinx seems to stringify types which is incompatible with equinox (cannot use stringified abstract annotations).
2. We set typing.GENERATING_DOCUMENTATION = True in conf.py to avoid expanding ArrayLike in the documentation (jaxtyping imports it as an Array instead). This change in imports lead to errors on isinstance checks.

Ideally doctest would be ran separately, outside a document generating context. At some point I might make the change to MKDocs, in which case another solution will need to be found for testing documentation anyway.