Add cut_diff example: structural editorial diff between two cuts

[chaoz23]

This adds an examples/cut_diff.py script that answers "what changed between cut A and cut B" — which clips were added, removed, retimed, moved, or shifted — in the spirit of existing examples like conform.py and shot_detect.py. The OTIO docs list "Shots Added or Removed From The Cut" as a first-class use case; this example implements it.

Because both inputs go through adapters, the cuts don't need to share a format — an EDL can be diffed against an FCP XML export of the revision:

$ python cut_diff.py editors_cut.edl finishing.fcpxml
1 retimed, 1 shifted (7 unchanged)
  ~ ZZ100_503A shortened by 12f (28f -> 16f)
  . ZZ100_504C shifted 12f earlier

Design notes:

• Clips are matched by identity (media target_url + source in-point), not timeline position — one insertion shifts every downstream timecode, so positional diffing reports everything as changed.
• "Moved" is detected by relative order (longest increasing subsequence over matched clips), so a gap inserted by a lift-trim doesn't read as every downstream clip moving.
• Ripple slides report as "shifted", separate from "retimed", so one trim doesn't read as N retimes.
• Scope is structural editorial only (clips/timing/order); effects and transitions are intentionally out, per their tool-specific serialization.
• --json output and diff(1) exit codes for scripting.

Validated against sample files from the cmx3600 and fcpx-xml adapter test suites, including hand-modified known-change cases. A packaged version with a test suite and an MCP server lives at chaoz23/otio-diff; this example is self-contained.

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[linux-foundation-easycla]

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• ✅ login: chaoz23 / name: chaoz23 (d92cd00)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.21%. Comparing base (73803ef) to head (1e9ceae).
⚠️ Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2030      +/-   ##
==========================================
- Coverage   84.58%   83.21%   -1.38%     
==========================================
  Files         181      180       -1     
  Lines       13306    13465     +159     
  Branches     1221     1253      +32     
==========================================
- Hits        11255    11205      -50     
- Misses       1868     2088     +220     
+ Partials      183      172      -11     

Flag	Coverage Δ
py-unittests	83.21% <ø> (-1.38%)	⬇️

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[jminor]

See also: #1922

[chaoz23]

Thanks — hadn't seen #1922. That's the ambitious integrated-tool path: an otiotool feature with a visual annotated-OTIO output, aimed at #26. From the outside it looks stalled, though — still a draft, no commits since Aug 2025, and currently conflicting with main.

This PR is deliberately narrower and at a different layer: a self-contained examples/cut_diff.py alongside conform.py and shot_detect.py. It touches no core code, CI is green, and it can land independently today. If #1922 revives later as the full integrated tool, this example points readers straight to it — they complement rather than compete. I've added a header note in the example cross-referencing otiotool/#1922 and #26.

Proposal: merge this as an example. If you'd rather hold it, I'll close it — no debate needed.