Cleanup

[nstarman]

Added type hints and docstrings.
Removed extraneous code.
Refactored the layout of some modules.
Moved the tests.

Requires #25

[nstarman]

We need to establish some tests (unit / integration / benchmark) so that we can check these PRs aren't messing with the code.

[nstarman]

All of the current tests assume data files. We need to make some similar tests with small data files we can host on the repo.

[codecov-commenter]

Codecov Report

Attention: 408 lines in your changes are missing coverage. Please review.

Comparison is base (c6d6c76) 0.34% compared to head (84ae21c) 0.32%.
Report is 3 commits behind head on main.

Files	Patch %	Lines
src/cats/cmd/_core.py	0.00%	61 Missing ⚠️
src/cats/pawprint/_footprint.py	0.00%	55 Missing ⚠️
src/cats/photometry/_base.py	0.00%	55 Missing ⚠️
src/cats/proper_motions.py	0.00%	49 Missing ⚠️
src/cats/photometry/_builtin/gaia.py	0.00%	41 Missing ⚠️
src/cats/photometry/_builtin/desi.py	0.00%	38 Missing ⚠️
src/cats/photometry/_builtin/ps1.py	0.00%	28 Missing ⚠️
src/cats/data.py	0.00%	23 Missing ⚠️
src/cats/pawprint/_core.py	0.00%	19 Missing ⚠️
src/cats/photometry/_builtin/__init__.py	0.00%	9 Missing ⚠️
... and 5 more

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Additional details and impacted files

@@           Coverage Diff            @@
##            main     #24      +/-   ##
========================================
- Coverage   0.34%   0.32%   -0.03%     
========================================
  Files          9      16       +7     
  Lines        864     929      +65     
========================================
  Hits           3       3              
- Misses       861     926      +65     

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[nstarman]

Suitable for squash merge!