Improve performance of adding package-manager sized directories to go-ipfs

[dirkmc]

See ipfs/kubo#6523

[dirkmc]

@andrew started work on a script we can use as the basis for generating a tree of files and dirs for performance testing. This makes 1024 files full of 1k random bytes in a folder call testing:
dd if=/dev/urandom bs=1024 count=1024 | split -a 4 -b 1k - testing/file.