Reconstruct probability distributions in new, qpd cutting code

[garrison]

Our current qpd cutting workflow allows a user to reconstruct expectation values. If a users wants instead to reconstruct probability distributions, they must use the older cutqc module for now. Resolution of this involves providing users an efficient way to extract desired properties of the probability distribution of the original circuit.

[garrison]

For the existing, expectation-value workflow, the original circuit should be free of Measure instructions (instead, observables are provided). In contrast, when one wants probability distributions, the original circuit will contain measurement instructions, and we'll have to keep track of them during cutting, particularly in the case where we must split the classical bits onto constituent backends (which is related to #220).