fix: fast memory/open file handle bail outs

[KillerCodeMonkey]

trafficstars

Please be kind :)

i only hacked it together, since i do not find any tests for the util methods. it is just an idea.

1. collecting everything for each "step" for each folder
2. remove tmp files with Promise.all - hopefully there are not that much
3. binary file check in chunks - so if there only a few files it runs in parallel, else batched
4. in the last step loop over all subfolders one by one and do step 1-4

Another idea: just provide an option to pass a callback that users can override the "walkAsync" method. Providing a "files to sign" method