public synchronized byte maxUsableProduceMagic() {
        return maxUsableProduceMagic;
    }
Maintains node api versions for access outside of NetworkClient (which is where the information is derived).
The pattern is akin to the use of {@link Metadata} for topic metadata.

NOTE: This class is intended for INTERNAL usage only within Kafka.
clients/src/main/java/org/apache/kafka/clients/ApiVersions.java