Port to Python 3.12

cerbero: Port from imp module to importlib module

imp module was removed in Python 3.12

We no longer need the site.py patch from setuptools because we use
a venv now.

cerbero: Fix bootstrap on Windows with Python 3.12

Fixes #427 (closed)

cerbero: Fix some warnings about escaping with Python 3.12

Stop using setuptools in a bunch of places, incl meson.recipe

Since Python 3.12, venv no longer installs setuptools by default, and
frankly we don't need it anymore since we can install with pip.

The only place left that uses setuptools is bundlesource now.