fix: handle Marshal error in CertificateResult.Hash()

[yasinlex]

Problem

CertificateResult.Hash() silently ignored the error from Marshal():

func (x *CertificateResult) Hash() []byte {
    bz, _ := Marshal(x)  // error ignored!
    return crypto.Hash(bz)
}

If marshaling fails, this returns a hash of nil bytes, which could lead to incorrect consensus decisions in the BFT protocol.

Changes

lib/certificate.go

• Hash() now returns ([]byte, ErrorI) instead of []byte
• Error from Marshal() is properly propagated

bft/bft.go (6 call sites)

• StartProposePhase(): compute hash before struct literal, return on error
• StartProposeVotePhase(): compute hash before sending vote
• StartPrecommitPhase(): compute hash before sending precommit
• StartPrecommitVotePhase(): compute hash before sending vote
• StartCommitPhase(): compute hash before sending commit
• CheckProposerAndProposal(): handle error when comparing hashes
• SafeNode(): handle error when validating HighQC

bft/msg.go

• GetValidateMessageParams(): handle error when computing results hash

controller/consensus.go

• Handle error when populating consensus summary

Impact

• Before: Marshal failure → hash of nil bytes → potential consensus divergence
• After: Marshal failure → error propagated → BFT handles gracefully