A producer emits 100 items fast into a Flow, and the collector takes 10ms per item. The flow is built with `flow { ... }.buffer(capacity = 0).collect { ... }`. Under the hood, what does `buffer(0)` (i.e. RENDEZVOUS) actually change versus a plain flow with no buffer operator?
flow {
repeat(100) { emit(it) }
}.buffer(0).collect { process(it) }