Integrate `WaveformTemplate`s into the rest of quil-rs

[antalsz]

Right now, quil-rs defines the WaveformTemplate trait, but doesn't actually make any internal use of it. We should provide integration between it and the rest of quil-rs; at a minimum, we should provide a function to parse a WaveformInvocation into a WaveformTemplate. This also unlocks the ability to write the unit tests in described in #406, and would overall help avoid problems like that encountered in #405.