Added support for large strain in pyFANS

[Snapex2409]

Added support for large strain in pyFANS, by reading in the strain_type from the reader.
This will construct an appropriate version of MaterialManager and Solver.
The results are stored in std::variant to reduce code duplication.

Furthermore, fixed the MPI implementation when using pyFANS in micro-manager.
Issue was: when running micro-manager using MPI it will create its own processes and will manage MPI. Each resulting rank will then manage a series of pyFANS instances. However, when using pyFANS in such a setting, it "sees" that there are other ranks in MPI_COMM_WORLD and will attempt to communicate with them.

But this is wrong, as it should only run in a single rank.
Fixed by introducing a communicator variable, that is set to either MPI_COMM_WORLD or MPI_COMM_SELF.

Checklist:

• I made sure that the CI passed before I ask for a review.
• I added a summary of the changes (compared to the last release) in the CHANGELOG.md.
• If necessary, I made changes to the documentation and/or added new content.
• I will remember to squash-and-merge, providing a useful summary of the changes of this PR.

[sanathkeshav]

@Snapex2409 make sure you are on the latest version of pixi by pixi self-update and then pixi lock.
When I ran it now after your last commit, it still changed the lock file. So that means the lock file is not upto date.

I somehow do not have permissions to push to your branch. Although I thought it should be allowed.