Obtain a two-qubit unitary's matrix in a way that will work after a qasm2 round-trip

[garrison]

Following Jake's comment at Qiskit/qiskit#12100 (comment), which should try replacing our use of Gate.to_matrix with a call to quantum_info.Operator(op).data. There should be a code comment right above this that says why this change was made (with a hyperlink). We should also add a test to circuit-knitting-toolbox/test/cutting/test_cutting_workflows.py to ensure that one can cut an arbitrary UnitaryGate after it has undergone a qasm2 round-trip.

This all was prompted by a test in #520 that had to be modified not to use XXPlusYYGate.

[garrison]

Looks like Jake has proposed a fix. We may not need to fix this at all on our end.

[garrison]

It looks like this will be fixed in Qiskit 1.1.1: Qiskit/qiskit#12523.

[garrison]

It might actually be worth doing this. If an Instruction consists of only gates, the Operator(op).data seems to work, but .to_matrix() does not. It's worth some additional investigation.