Read repair stale replicas

During a read, the coordinator gathers each replica's view of a key as [replica_id, version, value], where higher integer `version` is fresher and ties are broken by the lexicographically larger `value` (a deterministic last-write-wins conflict resolver). The winning (version, value) is the freshest under this rule. Return a list of replica_ids (sorted ascending as strings) that are STALE — i.e., whose (version, value) is not equal to the winning pair — because the coordinator must send them the repaired value. If all replicas already agree, return an empty list.