Async: an exception in the macrostep after the lock holder's own event is silently lost #689

On the async engine with catch_errors_as_events=False (the StateMachine default), when the lock holder's own event succeeds but a later microstep of the same macrostep raises (an internal event or an eventless transition), await send() returns the event's result and the exception is lost: no caller sees it and nothing is logged. The sync engine raises it to the caller of send().

class M(StateMachine):
    a = State(initial=True); b = State(); c = State()
    go = a.to(b); boom = b.to(c); back = c.to(a)
    def on_go(self): return "went"
    async def on_enter_b(self): await self.raise_("boom")
    async def on_boom(self): raise ValueError("kaboom")

• Sync (same chart with sync callbacks): sm.send("go") raises ValueError: kaboom.
• Async: await sm.send("go") returns "went", the machine stays in b, and the ValueError is not raised anywhere.

Reported as pre-existing on v3.2.1 in #688. Expected: the exception reaches the caller whose send() started the macrostep, as on the sync engine.