[WIP] Swap over to yara-x; improve performance and readability

[egibs]

After hacking around with yara-x locally last night, the performance gains over Yara are definitely noticeable (usually 2x faster at minimum).

I wanted to get this rather large refactor up to test the CI experience again since we have to build the API from scratch, but when refreshing the sample data locally I was down to about ~24-25 seconds with the integration tests taking about 27 seconds (on my M1 Pro MBP).

Edit, we're about 3-4x faster in GHA with 8-core runners:

go test -timeout 0 ./tests/...
ok  	github.com/chainguard-dev/malcontent/tests	49.979s

This is usually around ~170s.

That said, I plan on using 16-core runners to help with the yara-x build.

This PR also cleans up recursiveScan and fixes the behavior of longestUnique and splits out path-related functions into a new path.go file. Additionally, findFilesRecursively will locate files concurrently to help with large numbers of files.

Outside of the longestUnique changes, output is essentially 1:1 with the current implementation.