tractor/nooz/271.feature.rst

Add a per actor debug_mode: bool control to our nursery.

This allows spawning actors via ActorNursery.start_actor() (and other dependent methods) with a debug_mode=True flag much like tractor.open_nursery(): such that per process crash handling can be toggled for cases where a user does not need/want all child actors to drop into the debugger on error. This is often useful when you have actor-tasks which are expected to error often (and be re-run) but want to specifically interact with some (problematic) child.