Don't kill root's immediate children when in debug

If the root calls `trio.Process.kill()` on immediate child proc teardown
when the child is using pdb, we can get stdstreams clobbering that
results in a pdb++ repl where the user can't see what's been typed. Not
killing such children on cancellation / error seems to resolve this
issue whilst still giving reliable termination. For now, code that
special path until a time it becomes a problem for ensuring zombie
reaps.

tractor/_spawn.py

@@ -331,6 +331,7 @@ async def new_proc(
             bind_addr=bind_addr,
             parent_addr=parent_addr,
             _runtime_vars=_runtime_vars,
+            infect_asyncio=infect_asyncio,
             task_status=task_status,
         )
 
@@ -346,6 +347,7 @@ async def mp_new_proc(
     parent_addr: Tuple[str, int],
     _runtime_vars: Dict[str, Any],  # serialized and sent to _child
     *,
+    infect_asyncio: bool = False,
     task_status: TaskStatus[Portal] = trio.TASK_STATUS_IGNORED
 
 ) -> None: