Fix classical-bit handling in control-flow StochasticSwap

[jakelishman]

Summary

Previously we were expanding control-flow blocks to be full-width over all wires, and only contracting the qubits back again, without changing the clbits given as node arguments. This modifies the

The changes in most of the tests are necessary because the tests were testing behaviour that should be considered incorrect. The principal new test of all this behaviour is the additional assertions added in _visit_block in the random tests; these uniformly fail without this patch, and succeed with it.

Details and comments

Fix #8903.

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[coveralls]

Pull Request Test Coverage Report for Build 3282607050

• 12 of 12 (100.0%) changed or added relevant lines in 1 file are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.0003%) to 84.761%

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Files with Coverage Reduction	New Missed Lines	%
qiskit/extensions/quantum_initializer/squ.py	2	79.78%

Totals
Change from base Build 3282605851:	0.0003%
Covered Lines:	61946
Relevant Lines:	73083

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💛 - Coveralls

[mtreinish]

The code change looks good to me, but the one thing I think would be good is a dedicated test for this, or specifically with the follow-on effects to ensure we can serialize with qpy and qasm3 transpiled control flow circuits. Just to verify we don't regress this in the future, especially once we get sabre control flow aware.

[jakelishman]

This idea of writing post-transpile integration tests turned out to be an excellent idea - in trying to write them, I've already turned up more bugs in unrelated code than I was expected, such as #8923.

[jakelishman]

Added more tests in fb30ff8. They need all of:

• Fix BarrierBeforeFinalMeasurements with loose bits #8924
• Fix loose-bit handling in QPY #8928
• Fix single-bit-condition equality in QuantumCircuit and DAGCircuit #8930

to merge first before they'll pass, because of other bugs I found while writing the integration tests.

[jakelishman]

This PR should be ready to review and merge, now that its dependents are in.

[mtreinish]

LGTM, thanks for adding the extensive testing and fixing the long tail of issues it uncovered.