Make boxing_pass_manager() always use site="before" for meas/reset boxes

[Ian Hincks (ihincks)]

Summary

Right now if you specify the site as "after", this applies to all boxes found by the boxing pass manager. However, when you add site=after to a boxing containing measurements, the noise is not actually injected, but the signs are still reported.

Details and comments

Right now something like this

circuit = QuantumCircuit(2)
circuit.measure_all()

circuit = generate_boxing_pass_manager(inject_noise_targets="all").run(circuit)

actually ends up with a disconnected samplex. The one on the left is just reporting the noise signs, and nothing on the right is injecting noise.

[joshuasn]

lgtm, care to add a changelog?

[Ian Hincks (ihincks)]

Oh thanks. I have one written but not pushed.