Fix FieldVaryingPSF

[hugobuddel]

FieldVaryingPSF did not do anything at all because it used FieldOfView.image, which is otherwise unused, see AstarVienna/irdb#161

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 77.16%. Comparing base (d6758f6) to head (09eebc0).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
scopesim/effects/psfs/discrete.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #506      +/-   ##
==========================================
- Coverage   77.18%   77.16%   -0.02%     
==========================================
  Files          66       66              
  Lines        8205     8203       -2     
==========================================
- Hits         6333     6330       -3     
- Misses       1872     1873       +1     

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[hugobuddel]

@oczoske , I have commented out FieldOfView.spectrum (never used) and FieldOfView.image (only used by FieldVaryingPSF, which I fixed by making it use FieldOfView.hdu.data directly).

I've kept FieldOfView.cube for now. FieldOfView.cube seems to be only used by SpectralTraceList. All other Effects use fov.hdu.data directly, and it seems that this can also be done by SpectralTraceList. Is there a reason to keep FieldOfView.cube around, or can we remove it in favor of FieldOfView.hdu.data?

[teutoburg]

Ditching those specific (but (almost) unused) attributes in favor of the more general .hdu.data seems useful in this case 👍

[hugobuddel]

Hmm do I dear to merge this without checking the IRDB notebooks? Yeah for sure!