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

• [x] 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[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

Additional details and impacted files

```diff @@ 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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