Add support for a single feed

[slosar]

Description

Relax the requirement that there are always 2 feeds leading to 4 polarizations. Now allow for a single feed. Still require that there are Nfeed^2 polarizations.

Needs changelog and docs updates...

Motivation and Context

Types of changes

• 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.

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]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (a1ee29d) to head (6ea22be).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #394   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines         2019      2057   +38     
=========================================
+ Hits          2019      2057   +38     

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[bhazelton]

@slosar @nmahesh1412 Sorry for the slowness, but I think this is now in a place where it could be merged. You are the two users I know of who are most interested in this, so I wanted to see if either of you wanted to try it out and see if it works for you.

[slosar]

Hi Bryna, huh, I have completely forgotten about this, it was two years ago! :) In the mean time we have developed our own (harmonic-space) code to do the sims we need to do, so I do not need this feature and not even sure what to test. Perhaps @nmahesh1412 can help. I still think it is probably a good feature to have.