Tests

Simplify the structure of `CircuitSimulator` #786

Job	Run time
doctest	1m 16s
ubuntu-latest, python3.10, [email protected]	51s
ubuntu-latest, python3.10, [email protected]	3m 44s
ubuntu-latest, python3.11, qutip@master	5m 59s
windows-latest, python3.8, [email protected]	1m 44s
macOS-latest, python3.9, [email protected]	1m 8s
windows-latest, python3.8, qiskit+qir	2m 31s
macOS-latest, python3.9, qiskit+qir	1m 45s
ubuntu-latest, python3.7, qiskit+qir	1m 20s
Finalise coverage reporting	11s
	20m 29s

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