Create `.torrent` files for downloads

[tcely]

https://github.com/rndusr/torf

This requires stable names for the video file and associated files. I'd suggest generation of the metadata before moving the files to the generated names.

For example:

• {key}.{ext}
• {key}-thumbnail.jpg
• {key}.info.json

Creating a directory TubeSync-{extractor_key} containing appropriate files then creating a metadata file (TubeSync-{extractor_key}-{key}.torrent) should be clean enough that we don't need to regenerate the metadata later.

Implementation of this may also help with:

• [bug] can't download files which filename will exceed 255 characters #522 (comment)

  Maybe the best solution would be to first download the video with only its video ID as filename and rename it after it's completed to a max 255 chars filename.

• [feature] Ability to add debrid links instead of dl #549

  Creation of a magnet link and the ability to seed the existing .torrent may allow transfer of the files for caching by this type of service.

• Cooperative downloading by different TubeSync containers.