expandDeep uses unbounded queue internally which results in OutOfMemoryException when subscriber is not fast enough to keep up with publisher

Expected Behavior

not sure

Actual Behavior

OutOfMemoryException thrown

Steps to Reproduce

@Test
void reproCase() {
    val genBytes = { Array(1024 * 1024 * 100) { 0 } }
    val i = AtomicInteger(0)

    Flux. just(genBytes()).expandDeep({
        if (i.incrementAndGet() > 100)
            Flux.empty()
        else
            Flux.just(genBytes())
    }, 1)
   .delayElements(Duration.ofMinutes(5))
   .subscribe {
     println("byte array processed") 
   } 

}

Possible Solution

add variety of expand and expandDeep methods with bounded queue in order to limit memory usage

Your Environment

• Reactor version(s) used: 3.4.27
• Other relevant libraries versions (eg. netty, ...):
• JVM version (java -version): 11
• OS and version (eg uname -a): Windows 10