Implement DynamicsBackend.solve function and unit test

[donsano33]

Summary

Add public function DynamicsBackend.solve enabling ODE simulation with the preconfigured solver member of the DynamicsBackend.

Details and comments

I opted for the most barebone implementation, basically just mirroring the interface for the Solver.solve function with an additional validate parameter.

Depending on how sophisticated one wants to implement this function, a variety of extensions could be thought of, adding ease of usage but also complexity. One possible extension could be (similar to DynamicsBackend.run) to optionally use the placement of the Acquire pulses to dynamically figure out the t_span (if measurements are in the schedule / circuit).

Let me know if you want something of that kind to be added.

Closes #288

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