Cannot trim in the middle of a transition

[jminor]

When flattening multiple tracks into one, there are sometimes clips which overlap transitions on lower tracks, which leads to an error preventing the flattening operation. Specifically an exception is thrown and no result is returned.

Here is a repro case. This is a production example that was redacted with otiotool --redact to remove sensitive names, but the structure is left intact.

redacted.otio.zip

Repro steps:

• Download and unzip the attached redacted.otio file
• Run otiotool -i redacted.otio --flatten video -o flat.otio

Actual result:

Traceback (most recent call last):
  File "/Users/joshm/.local/bin/otiotool", line 8, in <module>
    sys.exit(main())
  File "/Users/joshm/.local/share/uv/tools/opentimelineio/lib/python3.9/site-packages/opentimelineio/console/otiotool.py", line 98, in main
    flatten_timeline(
  File "/Users/joshm/.local/share/uv/tools/opentimelineio/lib/python3.9/site-packages/opentimelineio/console/otiotool.py", line 601, in flatten_timeline
    flat_track = otio.algorithms.flatten_stack(tracks_to_flatten[:])
ValueError: cannot trim transition: Cannot trim in the middle of a transition

Expected result:
A flat.otio with one video track.

For the case of the bisected transition, the transition itself should be shortened, or discarded with a warning.