JP-4275: Store tweaked imaging WCS objects in mosaic for transfer to WFSS spectral images in assign_wcs

[tapastro]

Partially resolves JP-4275

This PR stores mosaic members' WCS objects along with their RA/Dec reference positions in i2d mosaic files. During processing of WFSS dispersed images, the WCS of the reference position closest to the dispersed image position is used in place of a fresh imaging WCS upon which we place the dispersed trace transform.

Tasks

• If you have a specific reviewer in mind, tag them.
• add a build milestone, i.e. Build 12.0 (use the latest build if not sure)
• Does this PR change user-facing code / API? (if not, label with no-changelog-entry-needed)
  • write news fragment(s) in changes/: echo "changed something" > changes/<PR#>.<changetype>.rst (see changelog readme for instructions)
    • if your change breaks step-level or public API (as defined in the docs), also add a changes/<PR#>.breaking.rst news fragment
  • update or add relevant tests
  • update relevant docstrings and / or docs/ page
  • start a regression test and include a link to the running job (click here for instructions)
    • Do truth files need to be updated ("okified")?
      • after the reviewer has approved these changes, run okify_regtests to update the truth files
• if a JIRA ticket exists, make sure it is resolved properly

[codecov]

Codecov Report

❌ Patch coverage is 17.64706% with 28 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.53%. Comparing base (2e5290f) to head (daa52df).

Files with missing lines	Patch %	Lines
jwst/assign_wcs/niriss.py	6.66%	28 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10593      +/-   ##
==========================================
- Coverage   86.58%   86.53%   -0.06%     
==========================================
  Files         374      374              
  Lines       40443    40476      +33     
==========================================
+ Hits        35018    35024       +6     
- Misses       5425     5452      +27     

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