Enable CI on CSCS (CUDA)

[RMeli]

This PR is a draft because it still requires some manual setup.

[Luthaf]

CI should be setup now!

[Luthaf]

cscs-ci run

[RMeli]

@Luthaf everything seems to be working. Up to you if you want to make the cscs-ci check mandatory or not for merging.

[Luthaf]

Don't pip install cupy, it needs to build from source and takes a very long time (hence the CI timeout). You can use bash scripts/install-cupy.sh, like in some other tox envs, which determines and then install the correct pre-built version

[RMeli]

cscs-ci run

[Luthaf]

Up to you if you want to make the cscs-ci check mandatory or not for merging

I think I set it up so it runs automatically for every PR targetting main, so it should show up in the list of checks by default

[RMeli]

Indeed. It might be a bit wasteful if a PR ends up with many new commits during the review process, but this CI is reasonably lightweight so it should be fine.