Fixes to FOV and implane-utils for correct flat_lamp scaling

[janusbrink]

After careful verification of scopesim_targets::Flat lamp behaviour these fixes to ScopeSim are needed so that extended sources are consistently rendered when the source pixel scale is changed and comparing 2+1D vs 3D (cube) source variants.

Note: Additional debug log prints were added, some may be too heavy to keep?

[codecov]

Codecov Report

❌ Patch coverage is 0% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 29.38%. Comparing base (45034ce) to head (55e9b07).
⚠️ Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
scopesim/optics/fov.py	0.00%	12 Missing ⚠️
scopesim/optics/image_plane_utils.py	0.00%	3 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (45034ce) and HEAD (55e9b07). Click for more details.

HEAD has 56 uploads less than BASE

Flag	BASE (45034ce)	HEAD (55e9b07)
	58	2

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1007       +/-   ##
===========================================
- Coverage   76.44%   29.38%   -47.07%     
===========================================
  Files          69       67        -2     
  Lines        9030     8906      -124     
===========================================
- Hits         6903     2617     -4286     
- Misses       2127     6289     +4162     

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