The biggest change in the dependencies is of course SQLAlchemy 2. On the
good side, we didn't need to do many code changes --- in regards to
actual Code, none!

On the better side, we now have way better type checking for SQLAlchemy
models, thanks to SQLAlchemy's integration with mypy (which we now
properly enable). Yay!

That also means though that many type hints needed to be updated, or
rather, the code using the SQL objects. Especially the difference
between Optional things and existing things has been clarified in a few
places, either by using sensible defaults, or by asserting that the
value is not None. That at least gives us an AssertionError instead of
an AttributError.