feat(mitigation): add TwoQubitPauliTwirlPass class

[pedrorrivero]

Summary

Adds new TwoQubitPauliTwirlPass class to perform Pauli twirling randomly on all two qubit gates of a circuit during transpilation.

Details and comments

• This is a utility class to avoid manual twirling in present and upcoming notebooks.
• There are plans for a notebook exposing how the class is built.
• Needed for the Utility Scaling notebook, demoed at IBM Quantum Practitioner's Forum 2023.
• Adds a number of internal auxiliary structures:
  • PauliTwirl class -- to represent a single Pauli twirl (i.e. pre- and post-operations plus an induced global phase).
  • generate_pauli_twirls function -- to compute operation-preserving Pauli twirls.
  • PauliTwirlPass parent class -- to perform Pauli twirling in all gates of the circuit (i.e. not just two-qubit gates).
  • A suite of related validation functions to handle user input smoothly.
• Adds an internal library of pre-computed Pauli twirls for all unparameterized two-qubit in the standard library today. This library is used for performance purposes (i.e. to avoid numerical re-computation of the twirls).

[coveralls]

Pull Request Test Coverage Report for Build 8057236981

Details

• 0 of 178 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 8031993973:	0.0%
Covered Lines:	182
Relevant Lines:	182

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💛 - Coveralls

[ashsaki]

Looks good to me. Nice job.