Py39 fix

[alex-rakowski]

adding back python 3.9 compatability, by using from __future__ import annotations in wpf.py, which has made it install with python 3.9 environment. I haven't run other tests, maybe @Steve could double-check?

[sezelt]

It seems pretty likely that before the usage of the new type hint syntax in wpf.py that we were Python 3.9 compatible.

As far as I know, we are not using match statements anywhere at the moment, but I can see them being super useful in a few places. I think a lot of code where we base our control flow on the shape of nested tuples could be improved that way, for example.

[alex-rakowski]

agreed, they'll be super useful. But until we use them, this PR will allow us to keep support for 3.9 with no rewrites as far as I can tell.

[bsavitzky]

It's definitely true that match could make some if/else clauses read a little more cleanly :)