feature: create a "hidden" a debug delegate that's automatically added in debug mode that polices the delegates

[weissi]

Historically we had many bugs like #348 where the delegate was called out multiple times "at the same time" (or didn't end up in a final state). This can be automatically checked and we should have a "hidden" delegate wrapper that just polices the guarantees (that we should also document) before calling into the actual user's delegate.

This can be in all debug mode runs everywhere.