A few updates to CommittedSubDag

[lxfind]

Needed by Sui.

[lxfind]

The Hash type is from fastcrypto, so we won't be able to implement it in Sui

[andll]

I also noticed that literally only place where we use the digest is info log in the consensus handler("Received consensus output..."). So instead of implementing Hash, should we just add Display trait on the ConsensusOutputAPI?

E.g. instead of ConsensusOutputAPI: Hash<DIGEST_SIZE>, we could do ConsensusOutputAPI: Display.

[lxfind]

Implemented Display instead