Fix: fix quorum calculation bug in HasQuorum function (#124)

[s-h-ubham]

Title: Fix Quorum Calculation Logic in HasQuorum Function

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Summary

This PR fixes a consensus bug in the HasQuorum function where quorum calculation incorrectly depended on the number of signers instead of the validator set size. The faulty logic required 100% voting power whenever there were fewer than 4 signers, which caused unnecessary stalls in valid scenarios.

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Background

The core IBFT library (consensus/ibft/validators.go) defines quorum based on validator set size (set.Len()), not the number of block signers. It provides two quorum calculation methods:

• LegacyQuorumSize: 2F + 1 formula (where F = max faulty nodes)
• OptimalQuorumSize: ceil(2/3 * N) formula

The buggy implementation in our code deviated from this by introducing a special case:

if valsCount < 4 {
    quorumSize = vs.totalVotingPower // ❌ Required 100% voting power
} else {
    quorumSize = getQuorumSize(...)
}

This caused valid blocks with sufficient voting power (e.g., 3 high-VP signers with 80% VP) to fail quorum checks when valsCount < 4.

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Changes Implemented

• Removed special case logic that enforced 100% voting power when signers < 4
• Always use getQuorumSize(blockNumber, totalVotingPower) for quorum calculation
• Ensured logic is now consistent with core IBFT consensus implementation
• Simplified HasQuorum for better maintainability

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Before (Buggy)

var quorumSize *big.Int
if valsCount < 4 {  
    quorumSize = vs.totalVotingPower  
} else {
    quorumSize = getQuorumSize(blockNumber, vs.totalVotingPower)  
}

After (Fixed)

quorumSize := getQuorumSize(blockNumber, vs.totalVotingPower)

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Benefits

• ✅ Bug Fix: Correctly passes quorum when sufficient voting power exists, even with fewer than 4 signers
• ✅ Consistency: Matches core IBFT library’s quorum rules
• ✅ Reliability: Prevents unnecessary chain stalls in larger validator sets
• ✅ Simplicity: Removes redundant logic and reduces risk of future bugs

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Testing

• ✅ All unit tests pass (TestValidatorSet_HasQuorum verified)
• ✅ Code compiles without errors
• ✅ Manual testing confirms correct quorum behavior in edge cases

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Impact

⚠️ Consensus Change — all validators must upgrade to avoid chain divergence.

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