Atomically sets the state(s) of one or more channels in a mix. The state map is a map of channels -> channel-state-map. A channel-state-map is a map of attrs -> boolean, where attr is one or more of :mute, :pause or :solo. Any states supplied are merged with the current state. Note that channels can be added to a mix via toggle, which can be used to add channels in a particular (e.g. paused) state.