It was only useful for doing #[embassy_executor::main(config = "config()")]`. Now that
it's gone, it makes more sense to build the config in main directly.
I've renamed the channel module for the MPMC as mpmc. There was a previous debate about this, but I feel that the strategy here avoids importing `channel::channel`. The change leaves `signal::Signal`, but I think that's ok. It is all a bit subjective of course. The bottom line for me is that I really like the term mpmc - it means something to me and aligns with broader naming e.g. in Tokio.
