moved find_clips function to superclass and added test case

[cato-o]

Summarize your change:
Moving find_clips to the Composition superclass so it only needs to be defined once. It was previously defined in both Track and Stack subclasses.

Reference associated tests:
Added a new test called "test_find_clips" to both test_stack_algo.cpp and test_track.cpp.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.79%. Comparing base (c0e97b0) to head (11ccc95).
Report is 58 commits behind head on main.

❌ Your changes status has failed because you have indirect coverage changes. Learn more about Unexpected Coverage Changes and reasons for indirect coverage changes.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1902      +/-   ##
==========================================
+ Coverage   84.11%   84.79%   +0.67%     
==========================================
  Files         198      177      -21     
  Lines       22241    12786    -9455     
  Branches     4687     1193    -3494     
==========================================
- Hits        18709    10842    -7867     
+ Misses       2610     1761     -849     
+ Partials      922      183     -739     

Flag	Coverage Δ
py-unittests	84.79% <100.00%> (+0.67%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/opentimelineio/composition.cpp	79.36% <100.00%> (+12.80%)	⬆️
src/opentimelineio/composition.h	83.87% <ø> (+18.35%)	⬆️
src/opentimelineio/stack.cpp	75.67% <ø> (+5.83%)	⬆️
src/opentimelineio/track.cpp	91.11% <ø> (+17.30%)	⬆️
src/opentimelineio/track.h	100.00% <ø> (ø)
...entimelineio-bindings/otio_serializableObjects.cpp	94.58% <100.00%> (+0.73%)	⬆️

... and 130 files with indirect coverage changes

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[darbyjohnston]

The changes look good, if you can rebase/merge your branch with the latest then I think this PR is ready. Thanks!

[cato-o]

Rebased and ready I think! Thank you :)