use the "ground" operation in PyZX to handle hybrid quantum-classical circuits

[dlyongemallo]

Right now, the transpiler separates operations natively supported in PyZX from those which aren't, optimises the subset which is supported, and then splices everything back together. In particular, this is a common pattern: circuit = [A, measure, B, conditional subcircuit], where only A and B are optimised.

It might be possible to handle the measure and conditional subcircuit parts using the "ground" operation in PyZX.

See this paper for details: https://arxiv.org/abs/2109.06071

[dlyongemallo]

This is blocked by pyzx not being able to convert "ground"s into measurements and classically-conditioned gates when extracting circuits.