RCAL-782: Changed image units.

[PaulHuwe]

Resolves RCAL-782

Closes #

This PR changes the units of the variables within the Image Model maker utilities and tests

NOTE: no regression test link, because these changes require update to regression test files.

Checklist

• [x] Added entry in CHANGES.rst under the corresponding subsection
• [x] 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 97.53%. Comparing base (087a60d) to head (ff860e4). Report is 5 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #327 +/- ## ========================================== - Coverage 97.56% 97.53% -0.03% ========================================== Files 30 31 +1 Lines 2788 2961 +173 ========================================== + Hits 2720 2888 +168 - Misses 68 73 +5 ```

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