Fix mypy Typing Issues

[ZephyrBlu]

Currently there are a lot of errors that occur when running mypy's type checker.

The important type information (Class attributes, function parameters, function returns) seems to be mostly fine, but other type information produces errors.

I'm almost certain this is due to me not understanding mypy's type system well enough, so I need to go through them one by one and figure out how to use mypy properly.