Add Mypy support

[inverse]

@ZENALC feel free to contribute - slowly going through the list, perhaps you'll have more insights :P

[ZENALC]

looks great :D

what do you think of upping the py v to 3.9+ and using built-in types?

so, we can do list[str] instead of importing List from typing :D

[inverse]

Could do but it might make it less accessible for people and current users of the product.

[ZENALC]

Yep, you're right. Let's just use normal type hints for now