Revise handling of classical register

[d1ssk]

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• Make sure you have tests for the new code and that test passes (run pytest)
• format added code and tests by black -l 120 <filename>
• If applicable, add a line to the [unreleased] part of CHANGELOG.md, following keep-a-changelog.

Then, please fill in below:

Context (if applicable):

In the previous handling of the classical register, the conversion to a circuit only succeeded if the node index was an integer sequence from 0 to the number of nodes.

Description of the change:

• In the to_qiskit method, the implementation was changed to use a dictionary that maintains the correspondence between the index of the classical register and the node index.
• This dictionary is added to the attributes of IBMQBackend and is also used when formatting the results of simulation or actual execution.
• A test was added in which random pattern is converted into qiskit circuit after processing Pauli measurements.

Related issue:
#12

also see that checks (github actions) pass.
If lint check keeps failing, try installing black==22.8.0 as behavior seems to vary across versions.