Allow SCA -1 to indicate that multiple images should be made.

[schlafly]

This PR adds a few assorted romanisim features:

• specifying SCA -1 to romanisim-make-image means looping over all 18 detectors
• Use a seed for the flat field implementation rather than making a separate draw for the flat field, to enable deterministic output.
• Improve the handling of WCS in output products.
• Instantiate the PSFs a little further from the corners of the WFI detectors
• Handle NaNs in positions and fluxes in catalogs by ignoring these sources.

[codecov]

Codecov Report

Attention: Patch coverage is 78.26087% with 5 lines in your changes missing coverage. Please review.

Project coverage is 92.21%. Comparing base (725b7cb) to head (790988c).
Report is 50 commits behind head on main.

Files	Patch %	Lines
romanisim/ris_make_utils.py	69.23%	4 Missing ⚠️
romanisim/wcs.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #109      +/-   ##
==========================================
- Coverage   92.44%   92.21%   -0.23%     
==========================================
  Files          16       16              
  Lines        1509     1593      +84     
==========================================
+ Hits         1395     1469      +74     
- Misses        114      124      +10     

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[PaulHuwe]

LGTM