Add MyPy checks and `py.typed` to enable typings support

[xSAVIKx]

While we already have some typings available it may be beneficial to configure MyPy in order to ensure type safety of the codebase as well as add the py.typed file to the repo to allow dependent projects to rely on the provided typings.

I'd say the following items should be covered:

• [ ] Add MyPy pre-commit hook to run MyPy automatically.
• [ ] Add all missing typings across the repository.
• [ ] Add py.typed into the module root.
• [ ] Ensure the MyPy check is required by the CI to merge PRs.