Adding support for MIRIAD calbiration tables

[kartographer]

Description

Adds a new class, MiriadCal, which supports reading of MIRIAD-based calibration solutions. As part of this, several functions from the UVData-based Miriad class have been moved over to aipy_extracts.py (added to the UV class) to allow for both UVCal and UVData objects from MIRIAD to use the same underlying functions.

Motivation and Context

SMA has a large stack of historic calibration tables in MIRIAD, and after pyuvdata added support for writing MeasurementSet-formated gains tables, there was some discussion about getting the read operation to work (both to cross-verify our own internal pipeline as well as to be able to carry forward work that had been previously done in MIRIAD). The existing AIPY interface -- and it's bindings to the uvio interface -- actually provided much of what was needed for reading this in, most of what was left was some relatively simple plumbing. Note that the ATCA test file actually has calibration solutions for three of the four types supported here, and was used fairly heavily in the testing phase of the code to verify that things were working.

(Also, this was this lowest-numbered issue I could close without knowing what an orthoslant is).

Closes #107.

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• 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 tutorial to highlight my new feature (if appropriate).
• I have added/updated tests to cover my new feature.
• I have updated the CHANGELOG.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a12cae9) to head (3377dfc).

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #1695      +/-   ##
===========================================
+ Coverage   99.84%   100.00%   +0.15%     
===========================================
  Files          68        69       +1     
  Lines       23506     23801     +295     
===========================================
+ Hits        23470     23801     +331     
+ Misses         36         0      -36     

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