Numpy.distutils has been removed in python >= 12

[louisl3grand]

Hi guys,

I tried to do a fresh install of plancklens and delensalot. There is an issue with the setup.py for both packages: the numpy.distutils functions has been removed in the newest python 3.12:
https://numpy.org/doc/stable/reference/distutils_status_migration.html#distutils-status-migration

We should do the migration to either setuptools, or to something more fancy (if fortran compilation is needed).
It does not seem super straighfoward to do, so I would let you to have a look at it when you have the time.