private long pollUnattached(long currentTimeMs) {
        UnattachedState state = quorum.unattachedStateOrThrow();
        if (quorum.isVoter()) {
            return pollUnattachedAsVoter(state, currentTimeMs);
        } else {
            return pollUnattachedAsObserver(state, currentTimeMs);
        }
    }
Attempt to send a request. Return the time to wait before the request can be retried.
raft/src/main/java/org/apache/kafka/raft/KafkaRaftClient.java