Switch to the walkdir crate

[ishitatsuyuki]

walkdir is a recursive directory traversing crate with no redundant operations (stat etc). It's also used by the award-winning ripgrep tool.

We always wanted the speed without complexity; how about reusing existing code instead of hand rolling one?

[BurntSushi]

ripgrep uses the ignore crate for a parallel walk, which is the same thing that fd uses. For single threaded mode, the ignore crate uses walkdir internally.

instead of hand rolling one

I don't see any hand rolled traverser in this repo.

[ishitatsuyuki]

Didn't notice that, thanks for correcting me.