Get rid of the Task Graph structure and convert design to use a Vec<TaskSet>

[rwails]

[robgjansen]

I've been aiming to remove all of the "Task" concept. The compiler should just return a Vec<Instruction> for a given role, i.e., implement this trait:

https://github.com/unblockable/proteus/blob/3bc360aefbb7a874921ccf06fc135c3d3387644c/src/lang/mod.rs#L41-L45

But to make that work, I think we need at least Wait and Notify instructions to help us cope with blocking during the handshake, and Jump to move the program counter to a different vec index.