Fix decomposition of an instruction with a single qubit and clbit

[Cryoris]

Summary

Fixes #8591.

Details and comments

Added a check to ensure the node that is replaced has the same number of classical bits that the rule we replace it with. Both these are required to be 0 right now as we don't have any gates that contain classical bits. I think this number could be allowed to be <= 1 though -- more than 1 would not necesssarily preserve the order?

[qiskit-bot]

Thank you for opening a new pull request.

Before your PR can be merged it will first need to pass continuous integration tests and be reviewed. Sometimes the review process can be slow, so please be patient.

While you're waiting, please feel free to review other open PRs. While only a subset of people are authorized to approve pull requests for merging, everyone is encouraged to review open pull requests. Doing reviews helps reduce the burden on the core team and helps make the project's code better for everyone.

One or more of the the following people are requested to review this:

• @Qiskit/terra-core

[jakelishman]

For substitute_node the number of arguments needs to be exactly identical, otherwise the connecting edges in the DAG change, and we'd need to do a larger contraction (which substitute_node_with_dag does). Strictly the limitations are actually that the rule has one one element and that the qargs/cargs are passed to the element are identical including order.

[coveralls]

Pull Request Test Coverage Report for Build 2926817522

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.003%) to 84.124%

---

Totals
Change from base Build 2922089833:	0.003%
Covered Lines:	56649
Relevant Lines:	67340

---

💛 - Coveralls