Function evaluate_key_evidence 

pub fn evaluate_key_evidence(
    key: &XorName,
    evidence: &KeyVerificationEvidence,
    targets: &VerificationTargets,
    config: &ReplicationConfig,
) -> KeyVerificationOutcome

Evaluate verification evidence for a single key.

Returns the outcome based on Section 9 rules:

• Step 10: If presence positives >= QuorumNeeded(K), QuorumVerified.
• Step 9: If paid confirmations >= ConfirmNeeded(K), PaidListVerified.
• Step 14: Fail fast when both paths are impossible.
• Step 15: Otherwise inconclusive.