infrastructure change needed for python modules

[Thomas Klausner <wiz%NetBSD.org@localhost>]

Hi!

The latest setuptools release points to an article which explains that
setup.py should not be used any longer, and what the replacements are:

https://blog.ganssle.io/articles/2021/10/setup-py-deprecated.html

I've noticed for some time that `setup.py test` were already broken
quite often, but it seems to me that 'setup.py build' and 'setup.py
install' should not be used any longer either. (They still work and
will probably keep working for some possibly quite long time.)

However, we do use setup.py for basically all python modules (see
lang/python/extension.mk, which is included by both distutils.mk and
egg.mk).

Can someone who's interested in Python and pkgsrc please convert
pkgsrc to current Python best practices?

Thanks,
 Thomas