Fast-forward cookiecutter, add CITATION.cff

[Zeitsperre]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes #xyz
• (If applicable) Documentation has been added / updated (for bug fixes / features).
• (If applicable) Tests have been added.
• CHANGELOG.rst has been updated (with summary of main changes).
  • Link to issue (:issue:number) and pull request (:pull:number) has been added.

What kind of change does this PR introduce?

• Updates the cookiecutter template to the latest version
  • Updates the Contributor Covenant to v3.0
  • Adds a CITATION.cff file
  • Removes black, blackdoc, isort
  • Modifies pyproject.toml for PEP 639-compliancy
• Pinned pydantic below v2.12 due to breaking changes

Does this PR introduce a breaking change?

No. black, blackdoc, and isort have already been removed here.

Other information:

The CITATION.cff file adds the authors from the Zenodo file. Names and affiliations need to be verified.