@Override
    public String toString() {
        return String.format(
            "Leader(localReplicaKey=%s, epoch=%d, epochStartOffset=%d, highWatermark=%s, voterStates=%s)",
            localReplicaKey,
            epoch,
            epochStartOffset,
            highWatermark,
            voterStates
        );
    }
Clear observer states that have not been active for a while and are not the leader.
raft/src/main/java/org/apache/kafka/raft/LeaderState.java