private ScheduledFuture<?> scheduleTimeout(long delay) {
            return executor.schedule(this, delay, TimeUnit.NANOSECONDS);
        }
Subscribes the given subscriber to this stream with timeout logic applied.

@param subscriber the subscriber to this stream
@param executor the executor for running timeout tasks and stream operations
@param options subscription options
@see StreamMessage#subscribe(Subscriber, EventExecutor, SubscriptionOption...)
core/src/main/java/com/linecorp/armeria/common/stream/TimeoutStreamMessage.java