Use numerical inverse to improve WCS accuracy

[schlafly]

There is an issue with the distortion reference files in CRDS such that wcs.world_to_pixel(wcs.pixel_to_world(...)) only inverts at the 0.05 pix level. That makes it impossible to do astrometry better than ~0.05 pix. This replaces wcs.world_to_pixel with wcs.numerical_inverse to avoid this issue. This is slightly slower, so we will restore the original approach when the reference file issue is resolved.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.21%. Comparing base (725b7cb) to head (dedd5e1).
Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #110      +/-   ##
==========================================
- 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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