reduce duplicate file scanning (rescan)

[soundsnow]

my files have never been added, so why do I have to repeat the scan every time

RetroArch Playlists (.lpl files) and Mupen 64 Plus FZ (Android Edition) only need to import the file paths once unless you add new games

only rescan manually when you add new files to the paths (including subdirectories)

If I have 15GB of files, the scanning time is particularly long (older hardware)

no one likes to spend so much time waiting for the same files to be scanned each time

https://github.com/mupen64plus-ae/mupen64plus-ae