Add RomVault ".dat" index format support

is your feature request related to a problem? Please describe.

Multiple projects like No-Intro, Myrient, Redump, MAME, TOSEC, ... use the ".dat"-file format from RomVault and DATVault for checksumming and integrity testing. This also allows people to build their collection with files from different sources while ensuring they've the same file.

List of indexing projects that use this format: https://wiki.romvault.com/doku.php?id=supported_dats

Describe the idea / solution you'd like

Would it be possible to implement support for these dat files in a way that allows:

• others to basically get a copy of the index (in this dat format) as if it was a regular file (e.g. in a /dats folder).
• to import/upload dat files to serve as index (manage the DATRoot) for files that should be there but aren't yet, e.g. if they're uploaded they will automatically appear under this file tree (aka be automatically sorted).
• to automatically update dat files in the background (when given via URL similar to how they're put into RomVault)
• to have the copyparty index stored in and/or synced to dat files.

Here is the link to the documentation for how RomVault does the scanning, and "fixing" (checking and moving files around): https://wiki.romvault.com/doku.php?id=scanning_fixing_levels

Edit: May help resolve #1395 as the dat format would allow to uniquely identify files and thereby make uploads deterministic (kinda).