Draft: Enable Python Testing

This MR has the goal to include the Python tests in the CI and expose them via meson to the command line.

Things done:

• CXX tests moved to their own suite cxx, Python to populate the python suite
• Add meson test definitions to the two existing Python tests

Things missing:

• I do not understand the interplay between meson, python and pip well enough to get this working properly. Right now, If I call pip install -e . && meson test --suite python the test work fine, but if I edit something and then re-call meson test --suite python they fail until I manually re-run pip install -e . - This certainly is not the goal?
• With above solved, this needs to be added to the CI, either as separate jobs or just running tests for all suites.