817: Added a pubsub channel implementation r=lulf a=diondokter
This is similar to Tokio's Broadcast channel, except that it doesn't allocate.
The publishers and subscribers are dynamic. They use an &dyn channel reference because it's really annoying to have to specify the mutex and const generics every time.
Do we need fully generic types as well?
Co-authored-by: Dion Dokter <diondokter@gmail.com>
Co-authored-by: Dion Dokter <dion@tweedegolf.com>