Fix mypy complaining about incompatible type for Z2 = Literal[0,1].

[dlyongemallo]

Partially addresses #62.

[jvdwetering]

Thanks for the fixes, but #62 refers specifically to type annotations for numpy objects, while your commit deals with some type:ignore's in other libraries. Which is still welcome of course!

[dlyongemallo]

You're right, I should've removed that comment or made it more clear. This PR started out by reversing commit d7db04a and fixing each line which had # type: ignore, but I wasn't able to repro the mypy errors which were actually due to numpy. It seems that the problem has actualy been fixed in mypy prior to version 0.990, which you're using.

Also, according to python/mypy#1424, the problems with hasattr are fixed in 0.991, so if/when you upgrade to that version, you can remove the # type: ignores from the lines with hasattr in the pyzx code as well.