Apply pre-commit hooks and add appropriate GitHub workflow

[peanutfun]

Changes proposed in this PR:

• Add GitHub workflow for checking pre-commit hooks
• Apply pre-commit hooks to repository

Things to note for reviewers:

• To review, follow the commits: The changes apart from re-formatting everything are
  • Newly added GitHub workflow for pull requests: Run pre-commit hooks on changed files (Executes in 2m to 20sec, thanks to caching)
  • Fix circular imports introduced by "mindless" isort sorting
• There are instances in the tests where the formatting could have been omitted (e.g., for larger arrays of test data). I simply did not care for time reasons 🤷

This PR fixes #

PR Author Checklist

• Read the Contribution Guide
• Correct target branch selected (if unsure, select develop)
• Descriptive pull request title added
• Source branch up-to-date with target branch
• Documentation updated
• Tests updated
• Tests passing
• No new linter issues
• Changelog updated

PR Reviewer Checklist

• Read the Contribution Guide
• CLIMADA Reviewer Checklist passed
• Tests passing
• No new linter issues

[emanuel-schmid]

replaced by idem-potent develop-black branch

[peanutfun]

@emanuel-schmid If I see this correctly, the workflow I added in this branch was not added to develop-black.

[emanuel-schmid]

@peanutfun oops! 😊 sorry I missed that. Will add it in a separate PR.