Build system improvements: use cmake and make pip installable

This replaces the Makefile with a cmake based build system and a scikit-build-core based packaging solution for the python bindings.

See:

• https://scikit-build-core.readthedocs.io/en/latest/ for what scikit-build-core provides for python bindings projects

TODO:

• Add more metadata in pyproject.toml (authors, dependencies, etc.)
• CI configuration
• Adapt dockerfile to new build system
• Update docs
• Remove Eigen from repository (not done for now, as it makes the diff of this PR unreviewable)

@xavier.rodrigues @marc.klinger Unfortunately, it seems am3 is already taken on PyPI: https://pypi.org/project/am3/

However, it looks like an inactive, empty project. I see two options:

• Try to contact the original author of that project (https://github.com/nriver/am3) and try to get access, if that doesn't help, open a request to take over the name at https://github.com/pypi/support.
• alternatively, use something like astro-m3 as the package name (this doesn't have to change the name of the library or the package).