torchvision removed the video read/write API in 0.23, so
`from torchvision.io import write_video` raises ImportError on
current torchvision (0.28). The symbol was never used - video
output goes through imageio's iio.imwrite in
save_video_with_imageio / save_video_with_imageio_lossless.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>