Tests

Simplify the structure of `CircuitSimulator` #787

Job	Run time
doctest	1m 59s
ubuntu-latest, python3.10, [email protected]	55s
ubuntu-latest, python3.10, [email protected]	3m 38s
ubuntu-latest, python3.11, qutip@master	6m 3s
windows-latest, python3.8, [email protected]	2m 5s
macOS-latest, python3.9, [email protected]	2m 6s
windows-latest, python3.8, qiskit+qir	2m 42s
macOS-latest, python3.9, qiskit+qir	1m 33s
ubuntu-latest, python3.7, qiskit+qir	1m 16s
Finalise coverage reporting	11s
	22m 28s

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