Miscellaneous updates following RTB review

[schlafly]

• Rename seed -> rng_seed in documentation.
• Extend documentation of "faintmag" in source generation.
• Input catalog PAs should be in degrees, not radians.
• Use dark_slope rather than dark image for simulation dark current.
• Revamp reference file & default parameter gathering.
• Issue a warning if --usecrds is not set.
• Support truncated exposures

[codecov]

Codecov Report

Attention: 37 lines in your changes are missing coverage. Please review.

Comparison is base (a3f71b7) 92.59% compared to head (510c55b) 92.43%.

Files	Patch %	Lines
romanisim/image.py	50.76%	32 Missing ⚠️
romanisim/l1.py	62.50%	3 Missing ⚠️
romanisim/ris_make_utils.py	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #99      +/-   ##
==========================================
- Coverage   92.59%   92.43%   -0.16%     
==========================================
  Files          16       16              
  Lines        1471     1494      +23     
==========================================
+ Hits         1362     1381      +19     
- Misses        109      113       +4     

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