Parallel test bug resolution

[aelanman]

Description

Generalizes parallel tests to run with different "root" processes. Writing this uncovered a bug in parallel pytest, which is also resolved here. Also adds a ParallelFlag class which isn't used, but might be useful. This provides a set of flags across all MPI processes which can be checked asynchronously by the root process.

Motivation and Context

Currently, parallelized tests which pass with Npus > 1 but fail with Npus == 1 will fail in general with pytest due to this bug. Ideally, the parallel marker means that a given test should be pass with the specified Npus, and whether or not it passes with Npus==1 is irrelevant.

Fixes #341

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Reference simulation update or replacement
• [ ] Documentation change (documentation changes only)
• [ ] Version change
• [ ] Build or continuous integration change

Checklist:

For all pull requests:

• [ ] I have read the contribution guide.
• [ ] My code follows the code style of this project.

Bug fix checklist:

• [x] My fix includes a new test that breaks as a result of the bug (if possible).
• [x] All new and existing tests pass.
• [ ] I have checked that I reproduce the reference simulations or if there are differences they are explained below (if appropriate). If there are changes that are correct, I will update the reference simulation files after this PR is merged.
• [ ] I have checked (e.g., using the benchmarking tools) that this change does not significantly increase typical runtimes. If it does, I have included a justification in the comments on this PR.
• [x] I have updated the CHANGELOG.

New feature checklist:

• [ ] I have added or updated the docstrings associated with my feature using the numpy docstring format.
• [ ] I have updated the documentation to highlight my new feature (if appropriate).
• [ ] I have added tests to cover my new feature.
• [ ] All new and existing tests pass.
• [ ] I have checked that I reproduce the reference simulations or if there are differences they are explained below (if appropriate). If there are changes that are correct, I will update the reference simulation files after this PR is merged.
• [ ] I have checked (e.g., using the benchmarking tools) that this change does not significantly increase typical runtimes. If it does, I have included a justification in the comments on this PR.
• [ ] I have updated the CHANGELOG.

[codecov[bot]]

Codecov Report

Merging #342 (05237d1) into main (d701412) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #342   +/-   ##
=======================================
  Coverage   99.01%   99.01%           
=======================================
  Files          13       13           
  Lines        1931     1931           
=======================================
  Hits         1912     1912           
  Misses         19       19           

Impacted Files	Coverage Δ
pyuvsim/utils.py	97.40% <ø> (ø)
pyuvsim/mpi.py	100.00% <100.00%> (ø)

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[aelanman]

@mkolopanis I just didn't want to delete it after writing it, but it doesn't need to be there. I'll remove it.

[mkolopanis]

I totally understand that. Never fun to write something, then throw it away.