Use the FastCDC::cut function to ask fastcd for cutting points as we
receive the data. Make sure to keep the last chunk in the temporary
buffer, as we might not actually cut at the end.
Also, use rayon to calculate the blake3 hash if the input data is
> 128KiB.
Change-Id: I6195f3b74eac5516965cb12d8d026aa720c8b891
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8135
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI