New Extractor Idea: `aria2` with bittorrents link/FTP/SFTP/Metalink download support

https://github.com/aria2/aria2

Would behave similarly to the wget extractor.

We should also consider extractors for:

- `rsync`
- `rclone`
- `icloudpd` https://github.com/icloud-photos-downloader/icloud_photos_downloader
- `zfs recv`
- `ssh `
- `lftp` https://github.com/lavv17/lftp

Start by reviewing the existing wget extractor and the aria2 project linked in the issue. Determine how aria2 should support BitTorrent, FTP, SFTP, and Metalink downloads, then define what matching the wget extractor's behavior means before considering the additional listed tools.

Written by the indexing model from the issue text.