Add decomposition check

[mikekryjak]

Built on top of #25

This PR adds two methods to HypnotoadGrid:

• check_decomposition tells you if the grid can be run on a particular number of cores or not. If not, it tells you a human-understandable reason why, so you can A) fix it and B) learn how the decomposition works.
• num_processors runs check_decomposition for several core counts up to max_procs and returns a list of how what core counts work. If you enable verbose, it will explain why each core count did or did not work.

This is based on the work of @bendudson in https://github.com/boutproject/ips-bout/blob/main/ipsbout/bout_worker.py#L89. The main change is that I simplified the structure of the code so it's more readable, and added the verbose descriptions.

This definitely should be in xBOUT, but since it needs HypnotoadGrid, I propose we move it all wholesale later. Also, since I have now prepared an explanation for each failure case, we should add these to BOUT++ as well so that the errors are more verbose.

To do:

• Implement functionality and test on MAST-U grid
• Test on the Hypnotoad test grids
• Implement test on all the test grids

Example output:

[ZedThree]

Looks useful! Sebastian was looking at adding something like this directly to BOUT++. It might be possible to work some magic to expose that functionality through boutpp, which would mean it would always be consistent with BOUT++.

I think this includes #25 ? Please could you just cherry-pick the relevant commits onto a new branch?

[mikekryjak]

I actually don't know what boutpp is. What does it do?
I can make a new branch with the commits.

[ZedThree]

boutpp is the Python wrapper for BOUT++, you can run models directly from Python.

[mikekryjak]

Added tests on the new test grids. Still no CI though. Ready for review