Concurrent safety of ReactiveGeneratorWrapper

[Sanne]

It would seem that our implementation of ReactiveGeneratorWrapper is at risk of producing duplicate identifiers when stressed under load.

I've been able to reproduce this stressing a Quarkus application on a modified Hibernate Reactive build (to better capture ids w/o needing to log them for uniqueness checks) and the trap triggers, however it requires significant wait times.

I'll see if I can distill an integration test which can reproduce such problems with higher chances.