chore: Convert feature segments models TestCase to a normal test function

[zachaysan]

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Changes

I'm working through re-writing the TestCase and APITestCase classes into normal test functions. I rewrote the existing classes and replaced with fixtures instead of recreating everything. There are other PRs that are similar to this one.

How did you test this code?

I manually changed the tests one at a time to refactor them as I went then ran the full test suite afterwards.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.98%. Comparing base (132ef77) to head (a90a02f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3925      +/-   ##
==========================================
- Coverage   95.98%   95.98%   -0.01%     
==========================================
  Files        1135     1135              
  Lines       36182    36159      -23     
==========================================
- Hits        34731    34708      -23     
  Misses       1451     1451              

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