feat(logic): implement parallel file restore

[aviallon]

On my SSDs, this speeds up file restoration by 1.1x to 3x.

Note: includes #132

[aviallon]

@Lazza if needed, I can drop the b9b9952 commit.

[Lazza]

I am wondering if it may be a good idea to implement these parts with asyncio instead. 🤔 Also reading the image file may benefit from that, as well.

[aviallon]

I am wondering if it may be a good idea to implement these parts with asyncio instead. 🤔 Also reading the image file may benefit from that, as well.

I tried experimenting with that, but it needs more changes first.
I think I'll come back to this PR a bit.

Perhaps I'll start by simply the conversion from a recursive call to a loop, and then I'll tackle async.