Draft support for reconstructing a probability distribution

[garrison]

This partially addresses #259 by supporting reconstructing of probability distributions in the special case where the circuit does not separate into disconnected components.

I plan to maintain this as a fork until we figure out how it should integrate with the existing code. (There might be some refactoring that would be appropriate before we integrate it.)

Demonstration notebook here.

I expect coverage to fail because I have not added tests (there's only the notebook for now), but adding tests should be pretty straightforward.

Remaining action items

• _decompose_qpd_measurements should throw an error if circuits already has a register called "qpd_measurements"
• update reconstruction for samplerv2
• change to 4-qubit GHZ state in the tutorial, perhaps
• add the tutorial to README.rst
• fix cut_wires to be compatible with classical registers

[coveralls]

Pull Request Test Coverage Report for Build 9142521182

Details

• 28 of 28 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.03%) to 95.504%

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Totals
Change from base Build 9104465513:	0.03%
Covered Lines:	3526
Relevant Lines:	3692

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💛 - Coveralls