Allow statevector simulation

[quantumjim]

From what I understand, Quantum Audio runs on counts via get_counts().

In Quantum Blur the corresponding function is circuit2probs, which now uses statevector simulation.

It would be good to allow the same method in Quantum Audio.

Perhaps we could use a special version of execute(), as we have for execute_with_sampler(). For this we could then modify get_counts() to construct a counts dictionary from the statevector when this method is used.