Cleanup mypy

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• I have read how to contribute to this project
• I have read the code of conduct to this project

Contributor checklist

• I am targeting the master branch and not the release branch (⚠️ very important)
• I have tested my contribution using ./run.sh
• I have tested my contribution using ./build.sh --flatpak-local --flatpak-install
• My contribution is fully baked and ready to be merged as is
• I ensure that all the open issues my contribution fixes are mentioned in the commit message of my first commit using the Fixes #1234 syntax

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Description

This cleans up all the existing mypy errors. In places where I couldn't really fix an issue, like some things with the gtk stubs, I explicitly ignored the error.

Type of Changes

	Type
✓	🔨 Refactoring