[tqwewe]

Great question, I did some digging into the source code of beam to help answer if signals should have special priority, and the conclusion (with the help of someone else from the elixir community) was that signals have no special priority over regular messages in beam. So I decided to take this same approach, where a regular message is just a `Signal::Message(M)` variant, and everything sent to the mailbox is a signal.

So gracefully shutting down an actor with `actor_ref.stop_gracefully().await` will process all pending messages before stopping. But the actor itself can be forcefully stopped with `actor_ref.kill()`