Initial pass at new pictureframe model

[drlaw1558]

This is an initial attempt at a new datamodel for the NIRSpec thermal picture frame reference file, see https://jira.stsci.edu/browse/CRDS-925

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.47%. Comparing base (4e83608) to head (6c36ad0).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #394      +/-   ##
==========================================
+ Coverage   78.16%   78.47%   +0.31%     
==========================================
  Files         115      116       +1     
  Lines        5144     5167      +23     
==========================================
+ Hits         4021     4055      +34     
+ Misses       1123     1112      -11     

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[drlaw1558]

Put this back to draft since there may still be some iteration on the file format over the next week or so.