Simplify StatePreparationAliasSampling tests by relying on Cirq simulators to simulate operations allocating ancillas

[tanujkhattar]

Fixes #6197

The two changes are

1. Use cirq.Simulator to simulate operations that can allocate new ancilla qubits
2. Update unary iteration implementation to proactively allocate all required ancillas so that a GreedyQubitManager is not required for an optimal ancilla allocation; and a SimpleQubitManager also works fine. This is useful because cirq.Simulator by default uses SimpleQubitManager to decompose operations and the trivial strategy results in all Unary Iteration based gates to allocate a LOT more ancillas than needed.

As part of looking into this issue, I also identified a general improvement that we can make to Cirq simulators s.t. for simulating operations that can allocate ancilla qubits, the simulation is optimized by potentially using SimulationProductState instead of StateVectorSimulationState to simulate the decomposed operations (right now, the former is used only at the top-level circuit simulation). But we can track this in a separate issue.

[mpharrigan]

lgtm