CI for openPMD

[franzpoeschel]

This adds openPMD-api to the CI infrastructure and adds a test for openPMD. At the moment, that test is test/shuffling_openpmd_test.py which tests openPMD-based shuffling.

It would be wise to add also a test that covers the basic functionality of openPMD I/O, especially also in parallel. Is there a test that uses numpy so far which I can modify to that purpose?

[franzpoeschel]

Looks good to me, I have some inline comments.
Given that parallel shuffling is now merged, should we maybe test that, too?

[DanielKotik]

@franzpoeschel @RandomDefaultUser If openPMD is an optional dependency for MALA, it should not be part of requirements.txt (instead add it here) and should only be added explicitly in the Dockerfile. If it is not an optional dependency, it should be present in requirements.txt and both mala_cpu_environment.yml and mala_cpu_base_environment.yml must then be updated accordingly. It must also be removed from the Dockerfile.

[RandomDefaultUser]

I think we are moving for it not to be an optional dependency, so I would suggest we do the latter. I can open an issue for this.

[franzpoeschel]

fixed by #541