Consider replacing `TypedDict` with `DataClass`es

In #52 we noticed that in #50 we'd missed adding a new field to the `PYPI_INDEX` typed dict in `reindex.py`. We should consider moving to `DataClass`es for this info so that we can't miss adding new fields in future changes.

Originally mentioned in https://github.com/napari/npe2api/pull/52#discussion_r2116063107