Better Express Timing Dependencies

[kalzoo]

Currently, any two instructions with InstructionRole::RFControl are presumed to operate on a frame and thus incur an ExecutionDependency::Frame between them during ScheduledProgram construction. However, that misses the point of this graph.

Each edge should express some condition to be satisfied in the scheduling of the program on a backend. In this case, what Frame means is ambiguous. A PULSE which follows a DELAY should follow it immediately; a SET-FREQUENCY which follows a PULSE can be executed at any time, subject to other constraints in the program. However, today, those two pairs are expressed the same way, with an ExecutionDependency::Frame.

Frame should be replaced with a combination of the existing StableOrdering and a new Timing:

• Timing between two instructions whose timing within the pulse program is governed by the Quil-T specification. That is, an instruction must start immediately following the end of the latest preceding instruction with which it shares a Timing edge in the graph.
• StableOrdering for all other cases, such as between a SET-FREQUENCY and PULSE.