RAD-148: Require exact datatypes for ndarrays

[WilliamJamieson]

for example RAD-1234: -->
Resolves RAD-148

Closes #353

Require exact datatype for ndarrays. This means that ASDF will not attempt to make any type casting when saving files, so all types are explicitly defined in the romancal code.

Checklist

• Schema changes discussed at RAD Review Board meeting
• Added entry in CHANGES.rst under the corresponding subsection
• Updated relevant roman_datamodels utilities and tests
• Passed romancal regression testing on Jenkins / PLWishMaster. Link: https://plwishmaster.stsci.edu:8081/job/RT/job/romancal/XXX/

[WilliamJamieson]

This confirms that exact_datatype is defined for all ndarrays.

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (e85f964) 95.32% compared to head (db2a02b) 95.38%.

Files	Patch %	Lines
tests/test_schemas.py	95.83%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #369      +/-   ##
==========================================
+ Coverage   95.32%   95.38%   +0.06%     
==========================================
  Files           4        4              
  Lines         171      195      +24     
==========================================
+ Hits          163      186      +23     
- Misses          8        9       +1     

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[WilliamJamieson]

There were a few errors in romancal unit tests with no regression test failures. The fixes for romancal are in spacetelescope/romancal#1090 and these fixes are independent of the changes here. To avoid any confusion the regression tests were run with the changes from 1090 so that there were no failures, see https://plwishmaster.stsci.edu:8081/job/RT/job/Roman-Developers-Pull-Requests/592.

[PaulHuwe]

LGTM