Replace ls-r with streaming version

Right now this module uses `ls-r`, but actually this lists all the files and then gives a callback. It would be faster if this would be streaming as such that files are processed as they come in.

Locate the module's use of `ls-r` and trace how its callback receives the complete file list. Check whether the existing project has tests or an entry point covering this behavior. Done means files are processed as they are discovered rather than after the full listing is collected.

Written by the indexing model from the issue text.