@Override
        public void subscribe(Subscriber<? super T> subscriber, EventExecutor executor,
                              SubscriptionOption... options) {
            requireNonNull(options, "options");

            final boolean withPooledObjects = containsWithPooledObjects(options);
            final boolean notifyCancellation = containsNotifyCancellation(options);
            subscribe(subscriber, executor, withPooledObjects, notifyCancellation);
        }
Returns the default {@link EventExecutor} which will be used when a user subscribes to a child
stream using {@link StreamMessage#subscribe(Subscriber, SubscriptionOption...)}.
core/src/main/java/com/linecorp/armeria/common/stream/DefaultStreamMessageDuplicator.java