Transitions: Add enabled flag

[natchar]

Fixes #1186

Added Enabled flag to Transitions.
Updated tests/test_transition.py

[codecov-commenter]

Codecov Report

❌ Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 84.51%. Comparing base (7adfb27) to head (d3e7aa7).

Files with missing lines	Patch %	Lines
...entimelineio-bindings/otio_serializableObjects.cpp	85.71%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2022   +/-   ##
=======================================
  Coverage   84.50%   84.51%           
=======================================
  Files         181      181           
  Lines       13225    13239   +14     
  Branches     1202     1202           
=======================================
+ Hits        11176    11189   +13     
- Misses       1866     1867    +1     
  Partials      183      183           

Flag	Coverage Δ
py-unittests	84.51% <94.44%> (+<0.01%)	⬆️

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

Files with missing lines	Coverage Δ
src/opentimelineio/transition.cpp	100.00% <100.00%> (ø)
src/opentimelineio/transition.h	100.00% <100.00%> (ø)
...opentimelineio/opentimelineio/schema/transition.py	100.00% <100.00%> (ø)
tests/test_transition.py	95.45% <100.00%> (+0.45%)	⬆️
...entimelineio-bindings/otio_serializableObjects.cpp	83.18% <85.71%> (-0.02%)	⬇️

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[timlehr]

Thank you @natchar! This looks good IMO.