Optimize file system walking

[haltcase]

Right now we use walkDirRec which traverses recursively into directories automatically. This means glob potentially walks over a lot of files that the given pattern might completely ignore. Instead it should probably use walkDir so that we can decide whether to recurse into the directories as we come across them.

[data-man]

Related RFC nim-lang/Nim#7077 😄

[haltcase]

@data-man thanks although I ended up basically modifying walkDirRec and adding logic as needed. Any chance you could check out the PR? I want to run a comparison test on a fairly large directory structure before merging, but it should be good otherwise.

(this reminds me I still need to set up CI)