feat: generate videos that play a clip of the source video

[saraburns1]

Description

Video blocks can be set to play only a clip of the source video (start/end time in Studio). The edx-platform video player then reports length as the clip duration (endTime - startTime) but time against the full source video, which made Aspects show positions past the end of the video.

This generates that case so load and test data cover it:

• About 25% of generated videos are clips: start between 10–60s, at least 60s long, ending within the 195s source video (VIDEO_CLIP_* in constants.py).
• Video events for clipped videos report the clip length, and positions between the clip start and end in the source video, as the real player does. Unclipped videos are unchanged.
• Course block data for every video includes video_start_time and video_end_time (0.0 when not clipped), matching what the course block sink sends.

Related:

• feat: add video clip start and end times to course block data platform-plugin-aspects#259 sends the clip times from the LMS.
• fix: shift video positions to the start of video clips aspects-dbt#179 shifts the positions in Aspects using them.

Testing

• Added tests for clipped and unclipped video events and block data, and for the generated clip bounds. The full suite passes (76 tests), and pylint, pycodestyle, pydocstyle, mypy and isort are clean.
• Manually: load data into an Aspects instance with aspects-dbt#179 applied. Video positions and watched segments for clipped videos should stay within the clip length.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.67%. Comparing base (9f7cac1) to head (2a4149f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #275      +/-   ##
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+ Coverage   85.54%   85.67%   +0.12%     
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  Files          29       29              
  Lines        1986     2004      +18     
  Branches      175      175              
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+ Hits         1699     1717      +18     
  Misses        260      260              
  Partials       27       27              

Flag	Coverage Δ
unittests	85.67% <100.00%> (+0.12%)	⬆️

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