MultiFab tutorial with pyamrex

[EZoni]

Thank you to @RevathiJambunathan, @oshapoval, @dpgrote, @kngott and @ax3l for the teamwork.

Rewrite the "MultiFab" guided tutorial using pyamrex. Outstanding questions marked as "TODO" comments.

[etpalmer63]

Looks super cool!

Just a reminder, that if you want to add the example to the CI/CD testing, the method for build and test for the Python code is likely different than the existing examples.

[EZoni]

Sounds good, thanks! Yes, I'm not sure how tutorials are treated with respect to CI/CD testing in AMReX. I will probably discuss this with @WeiqunZhang or @atmyers during the next part of the NERSC hackathon later this week.

[EZoni]

@ax3l @RevathiJambunathan @kngott

I think this is ready for review. The test now shows both ways to fill an array on a given box (NumPy operations and standard for loop over box indices), and compares two arrays filled with these methods.

I'm also using the function write_single_level_plotfile now available in pyamrex, as well as the IOProcessor function to make sure that we print only from the IO process.

[ax3l]

I finalized the example TODO markers and added CI :)

[ax3l]

Documentation added as well :)

[ax3l]

@EZoni @atmyers @etpalmer63 ready to go :)

[ax3l]

@EZoni @atmyers @etpalmer63 @WeiqunZhang ping :)