Use mult for the closing channel

Mult allows for multiple consumer channels for a single value. Plain
channels on the other hand will only ever have a single produced value
taken by a single consumer even if the channel is shared across multiple
go expressions.
Add unbind-sync! for unbinding synced atom paths
.off on ref and event alone

Seems like passing the callback used for .on into .off isn’t working.
Events are still being pulled from the channel.
Cleanup