[torchvision] Move video utilities to internal fb/io location

[NicolasHug]

Summary:
This diff moves the torchvision.io video utilities (read_video, write_video, read_video_timestamps) from the OSS location to the internal fb/io location.

Changes:

• Created fb/io/video.py with the full implementation of video functions
• Updated fb/io/init.py to export video functions and internal helpers
• Updated torchvision/io/init.py to import video functions from fb/io
• Made torchvision/io/video.py a stub that re-exports from fb/io/video.py
• Removed video functions from torchvision.io.all (for OSS)

This change ensures:

• Internal users can continue using 'from torchvision.io import read_video'
• Internal users importing from torchvision.io.video directly still work
• No BUCK changes are required
• OSS/GitHub users will no longer have access to these deprecated video APIs

Differential Revision: D95933713

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/vision/9433

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❌ 2 New Failures, 1 Pending, 3 Unrelated Failures

As of commit c9b4a25 with merge base 6d85459 ():

NEW FAILURES - The following jobs have failed:

• Build Linux Wheels / pytorch/vision / upload / upload-manywheel-py3_10-rocm7_1 (gh)
  ##[error]Response status code does not indicate success: 503 (Service Unavailable).
• Build Windows Wheels / pytorch/vision / build-wheel-py3_10-cuda12_6 (gh)
  Process completed with exit code 1.

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• Build Windows Wheels / pytorch/vision / build-wheel-py3_10-cuda12_8 (gh) (trunk failure)
  Process completed with exit code 1.
• Build Windows Wheels / pytorch/vision / upload / upload-wheel-py3_10-cuda12_6 (gh) (trunk failure)
  Unable to download artifact(s): Artifact not found for name: pytorch_vision__3.10_cu126_x64
• Build Windows Wheels / pytorch/vision / upload / upload-wheel-py3_10-cuda12_8 (gh) (trunk failure)
  Unable to download artifact(s): Artifact not found for name: pytorch_vision__3.10_cu128_x64

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[meta-codesync]

@NicolasHug has exported this pull request. If you are a Meta employee, you can view the originating Diff in D95933713.