protofsm: allow multiple internal events to be emitted

In this commit, we update the execution logic to allow multiple internal
events to be emitted. This is useful to handle potential out of order
state transitions, as they can be cached, then emitted once the relevant
pre-conditions have been met.

protofsm/state_machine_test.go

@@ -80,7 +80,9 @@ func (d *dummyStateStart) ProcessEvent(event dummyEvents, env *dummyEnv,
 		return &StateTransition[dummyEvents, *dummyEnv]{
 			NextState: &dummyStateStart{},
 			NewEvents: fn.Some(EmittedEvent[dummyEvents]{
-				InternalEvent: fn.Some(dummyEvents(&goToFin{})),
+				InternalEvent: fn.Some(
+					[]dummyEvents{&goToFin{}},
+				),
 			}),
 		}, nil