JP-4370: Unset S_REGION if wcs is not sky-like

[melanieclarke]

Resolves JP-4370

NIRSpec lamp exposures are resampled in the MSA frame, not in RA/Dec, so they should not have a celestial S_REGION assigned after assign_wcs.

This PR uses a utility that checks the output coordinate frame for the WCS to see if any of its units are sky-like (degrees or arcsec). This utility was previously in the resample module; I moved it to the assign_wcs.util module, near the s_region utility functions used in multiple places.

Tasks

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  • update or add relevant tests
  • update relevant docstrings and / or docs/ page
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      • after the reviewer has approved these changes, run okify_regtests to update the truth files
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[codecov]

Codecov Report

❌ Patch coverage is 94.11765% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 86.58%. Comparing base (2e5290f) to head (5cceb00).

Files with missing lines	Patch %	Lines
jwst/resample/resample_spec_step.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #10586   +/-   ##
=======================================
  Coverage   86.58%   86.58%           
=======================================
  Files         374      374           
  Lines       40443    40453   +10     
=======================================
+ Hits        35018    35027    +9     
- Misses       5425     5426    +1     

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[melanieclarke]

Regtests:
https://github.com/spacetelescope/RegressionTests/actions/runs/26840478323

Results are as expected. NIRSpec lamp exposures no longer have S_REGION keywords after assign_wcs. Other products are not affected.