Allow for mid-circuit correction

[nonhermitian]

M3 can mitigate mid-circuit measurements, provided that the results are not used until the end, e.g. no controlling gates based on the measured outcomes. Those cases need per-shot correction.

I think we are already setup for this, but we need a new routine that looks for correctable mid-circuit measurements. Something like a generic measurement_mapping to go with final_measurement_mapping?

[nonhermitian]

This is actually a bit more difficult than I thought because one can duplicate physical qubit indices, which means that they cannot be used as keys in the mapping directly

[nonhermitian]

This was done in #133