WCU flux mismatch

[oczoske]

This started out with the observation that the flux of the laser lamps through the pinhole mask of the METIS WCU was too low (#850). While looking into this it was noticed that the background flux (with lamp off) without and with a focal-plane mask inserted was not identical. The expected ratio is 0.95, which is the emissivity of the integrating sphere, whereas the emissivity of the (opaque parts of the) focal-plane mask is taken to be 1. The observed ratio was more like 20. This PR makes these values consistent by setting the values of the holehdu and opaquehdu, which define the FPMask, in terms of pixels rather than solid angles as before.

While consistent, it is currently not clear that it is also correct. Running the METIS_WCU.ipynb notebook shows that the signal from the black-body source through the open FPMask is lower than it used to be. If that is true, then the problem may be not with the FPMask but with the black-body source (which is a TERCurve without an hdu). Update: The difference can be explained through the new pupil mask (PPS-LM instead of open) and averaging and gain of the detector readouts. The notebook still needs to be updated.

Closes #850

[codecov]

Codecov Report

❌ Patch coverage is 70.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.87%. Comparing base (db13ad2) to head (09e95d3).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
scopesim/effects/metis_wcu/metis_wcu.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #860   +/-   ##
=======================================
  Coverage   74.87%   74.87%           
=======================================
  Files          69       69           
  Lines        8863     8867    +4     
=======================================
+ Hits         6636     6639    +3     
- Misses       2227     2228    +1     

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[teutoburg]

I don't know nearly as much about the WCU stuff as you, so if you say it's now less inaccurate than before, that's good. Don't see any obvious issues code-wise 👍