[RFC] Folder handeling and multi threadings

[BuyMyMojo]

This is a messy implementation not really meant to be pulled into the main branch.

I was messing around with adding support for processing entire folders for comparing videos and along the way I decided to add masic tokio based threading since ssimulacra2 is a single threaded process.

This does add two extra deps and tokio is a bloated one since I have it set to full right now while I mess around so it doesn't follow the desire to keep this a minimal executable.

Just sharing these changes for comment and sharing of ideas.

[Luni-4]

@BuyMyMojo and @shssoichiro

Is there any update for this one?