reactor-core: Map and flatMap operator chaining is not stack-safe

Expected behavior

Chaining large numbers of map and flatMap operators is stack-safe

Actual behavior

StackOverflow on MonoMapFuseable.subscribe

Steps to reproduce

Mono<Integer> initial = Mono.just(0);

for (int i = 0; i < 5000; i++) {
	int currentI = i;
	initial = initial.map(previous -> currentI);
}

assert initial.block() == 5000;

Yields a StackOverflow error:

java.lang.StackOverflowError
    at reactor.core.publisher.MonoMapFuseable.subscribe(MonoMapFuseable.java)
    at reactor.core.publisher.MonoMapFuseable.subscribe(MonoMapFuseable.java:59)
    at reactor.core.publisher.MonoMapFuseable.subscribe(MonoMapFuseable.java:59)
    at reactor.core.publisher.MonoMapFuseable.subscribe(MonoMapFuseable.java:59)
    at reactor.core.publisher.MonoMapFuseable.subscribe(MonoMapFuseable.java:59)
    at reactor.core.publisher.MonoMapFuseable.subscribe(MonoMapFuseable.java:59)
    at reactor.core.publisher.MonoMapFuseable.subscribe(MonoMapFuseable.java:59)
        ...

Reactor Core version

3.1.8.RELEASE

JVM version (e.g. java -version)

1.7 with Kotlin in the project, 1.8 in the system