RCAL-831: Add statistics field to TVAC and FPS Models

[PaulHuwe]

Resolves RCAL-831

Closes #

This PR adds statistics blocks to the TVAC and FS models.

Checklist

• Added entry in CHANGES.rst under the corresponding subsection
• updated relevant tests
• updated relevant documentation
• Passed romancal regression testing on Jenkins / PLWishMaster. Link: https://plwishmaster.stsci.edu:8081/job/RT/job/romancal/XXX/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.52%. Comparing base (087a60d) to head (181671a).
Report is 22 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #351      +/-   ##
==========================================
- Coverage   97.56%   97.52%   -0.05%     
==========================================
  Files          30       37       +7     
  Lines        2788     3347     +559     
==========================================
+ Hits         2720     3264     +544     
- Misses         68       83      +15     

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[schlafly]

LGTM, thanks!