Support more WCS types

[schlafly]

Folks doing simulations outside romanisim may want to use WCSes other than the romanisim GWCS, gwcs, or galsim.roman.WCS. This adds support for a generic FITS header.

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.20%. Comparing base (d18949b) to head (8d20487).
⚠️ Report is 15 commits behind head on main.

Files with missing lines	Patch %	Lines
romanisim/wcs.py	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #346      +/-   ##
==========================================
- Coverage   89.63%   89.20%   -0.43%     
==========================================
  Files          17       17              
  Lines        2633     2669      +36     
==========================================
+ Hits         2360     2381      +21     
- Misses        273      288      +15     

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[PaulHuwe]

LGTM