Extract calibration modules from the reader

[mraspaud]

This PR extracts calibration modules from the reader.

As we are preparing to add new calibration and navigation algorithms for pygac, it needs to be upgraded to be made more modular.

[codecov]

Codecov Report

Attention: Patch coverage is 98.12734% with 5 lines in your changes missing coverage. Please review.

Project coverage is 76.11%. Comparing base (298252f) to head (806fec3).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
pygac/reader.py	95.57%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #127      +/-   ##
==========================================
+ Coverage   74.22%   76.11%   +1.89%     
==========================================
  Files          33       32       -1     
  Lines        3115     3195      +80     
==========================================
+ Hits         2312     2432     +120     
+ Misses        803      763      -40     

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[sfinkens]

Nice work! I like the entry-point approach. Should have started reading with the tests, they are pretty clear 👍

[mraspaud]

@sfinkens if you could review again, that would be great :) I have address all you comment I think, and did some more refactoring. I need to do more, but I will do that in another PR, along with extracting the navigation module.

[sfinkens]

Very nice, thanks for all the refactoring effort!