This introduces a new struct, B3Digest, which internally holds a
Vec<u8>, but only allows construction with 32 bytes.
It also implements display, which will print the base64 representation.
This should reduce some boilerplate when parsing Vec<u8>.
Change-Id: Ia91aa40cb691916773abc8f93e6ed79a5fd34863
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8592
Reviewed-by: tazjin <tazjin@tvl.su>
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
