Proof of concept McStas-mini scikit-build-core pkg

[tkittel]

As discussed with @willend it would be useful (and hopefully not difficult) to add a small subdirectory with infrastructure for installation via python tools like pip.

Specifically I am thinking about a pyproject.toml + scikit-build-core + a few small python wrapper files.

To be used in e.g. a jupyter notebook like:

%pip install "git+https://github.com/mccode-dev/McCode#subdirectory=meta-pkgs/pypkg
import mcstas
mcstas.init()#<--- sets $MCSTAS and possibly other stuff
!mcrun --help

This would probably best work for use-cases without MPI and on platforms where build tools have already been installed (like github CI platforms or in google collab).

Whether or not this would end up as proper prebuilt PyPI pkgs etc. would be something we decide later once we get a feel for how it works.