Fix some mypy warnings

[KapJI]

Proposed change

Even though there are type hints, mypy is not run to check them. I fixed some issue but there are many more, please help me to fix them.

Also isort wasn't run in CI and it was missing configuration, added that.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New feature (which adds functionalit)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• Local tests pass.
• There is no commented out code in this PR.
• The code has been formatted using Black (make black)
• Tests have been added to verify that the new code works.

[KapJI]

@ludeeus are you interested in fixing this?

[KapJI]

@ludeeus ping

[ludeeus]

Replaced by #76