Added Polarization Conversion Functions to and from Celestial frame

[s0larish]

• Added to_celestial and from_celestial functions to convert polarization to and from celestial frames within starfield removal in Level 3.
• Added tests for these two functions.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.25%. Comparing base (3903207) to head (bc72be8).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #328      +/-   ##
==========================================
+ Coverage   86.98%   87.25%   +0.27%     
==========================================
  Files          56       56              
  Lines        3718     3799      +81     
==========================================
+ Hits         3234     3315      +81     
  Misses        484      484              

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