We can drop most of Hasher if we use a MultiWriter writing to the hash
function and a minimal CountingWriter.
This should make things a bit more understandable.
Change-Id: I37ee72d9a5c73f253aecc1ad761cb723389b89fc
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9529
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: Connor Brewster <cbrewster@hey.com>
Tested-by: BuildkiteCI