TST: Reorganize the entire test module.

[zssherman]

Reorganize test module so that each module has its own test file. This allows for separation and easier debugging. Also fixed a few functions missing from init.py 's and broken tests etc.

• Closes Reorganize the Unit Tests #731
• Tests added
• Documentation reflects changes
• PEP8 Standards or use of linter
• Xarray Dataset or DataArray variable naming follows 'ds' or 'da' naming

[AdamTheisen]

looks good! Thanks for the effort here! We should double check the unit test coverage results before merging to make sure everything lines up with expectations

[zssherman]

@AdamTheisen So some of the tests break due to overlap in naming, I suggest and changed the names of overlapping test to match the module so test_arm.py in io and test_arm.py in qc, now test_arm.py in qc is test_arm_qc.py to fix the overlap.