Test with PyICU timezones [Python, guided by maintainer]

[niccokunzmann]

At the moment, we check icalendar with zoneinfo and pytz. We can also make sure that PyICU works.

• [ ] create a TimzoneProvider for PyICU
• [ ] parametrize the tests to work with PyICU (conftest.py)
• [ ] add possible additional tests

[devdanzin]

For anyone trying to tackle this, building PyICU can be a hassle, so I suggest either using Anaconda or trying a wheel from https://github.com/cgohlke/pyicu-build/releases.