chore: add pre-commit

[langenhagen]

Add the pre-commit system to conveniently manage sophisticated git pre-commit hooks for quick local checks fore pushing. Upshot is, you don't have to wait for CI to tell you that e.g. formatting or typing is wrong.

The pre-commit project provides a fairly easy way to maintain several different hooks. You can use standard checks, write your own or use community-driven checks that are usually hosted on GitHub and configure them to your gusto.

I added simple ruff-related checks, taken from:
https://github.com/astral-sh/ruff-pre-commit

I also enabled 2 standard checks, one for trailing spaces and another one for JSON-verification.
We can add type checking with mypy as well, but that seems not to be set up properly atm.

Usually, hooks work on the changeset/diffs of the commit, although that depends on the individual hook. Some might work across entire files or the entire repo. You can configure most of them.

Note that pre-commit hooks do bring their own dependencies, managed in a separate venv, that is not the project's actual venv. This way, depencencies and dependency version in the hooks may deviate from the actual project's setup.

Useful commands:

pre-commmt install      # install the hooks into this mf
pre-commit run --all    # run the checks against all files in the repo
git commit --no-verify  # --no-verify: bypass pre-commit checks

See: https://pre-commit.com/