Use zoneinfo stdlib as the timezone provider.

New excluded test currently also fails on 6.1.2.

Signed-off-by: David Runge <dvzrv@archlinux.org>

Remove unnecessary quotes and curly braces.
Do not break long lines.
Remove tests from package in package().

Simplify installation in package() to adhere to python package guidelines.

https://archlinux.org/todo/cleanup-of-python-setuptools-dependency-for-console-scripts/

Switching to python-pytest for the test suite.
Moving python-setuptools to depends, as there is an entry_point.

Upgrading to 4.0.4. Updating maintainer info. Adding python-setuptools to optdepends for icalendar executable. Minor cleanups.