Move some image parsing logic

[cshanahan1]

Move part of the image parsing logic to its own function to avoid an issue in Background one_sided/two_sided.

Background.one_sided/two_sided were calling an instance method from _Image_Parser. This works as is, but if you were to then try to call another instance method from within that one, it does not understand 'self' and will cause an error. I moved the bit of code that Background needed to its own function to avoid this issue (which doesn't exist in main yet, but does in work on another branch I have).

Also fixed a bug where checking if data was u.quantity.Quantity was never triggered because the check for np.ndarray happened first.

I don't think this needs a change log.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (715361e) 81.77% compared to head (b2e032f) 81.92%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #209      +/-   ##
==========================================
+ Coverage   81.77%   81.92%   +0.15%     
==========================================
  Files          10       10              
  Lines        1004     1007       +3     
==========================================
+ Hits          821      825       +4     
+ Misses        183      182       -1     

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[tepickering]

looks good! only comment would be to tweak the test to cover the missed line that codecov flagged.

[cshanahan1]

looks good! only comment would be to tweak the test to cover the missed line that codecov flagged.

i added some coverage and realized in the process that the isinstance(image, u.quantity.Quantity) was never actually being triggered because isinstance(image, np.ndarray) was being checked first. It didn't seem to cause any noticeable issues since this already existed on main, but I fixed it just in case.