Expose `stim.FrameSimulator` to python API

[Strilanc]

Sometimes you just want to propagate errors without worrying so much about the reference sample.

Features:

• Optional frame randomization during collapse.
• Read/write the pauli strings being propagated.
• Measurement flip record.
• Detector / observable record?

[danielbarter]

Now I understand why pauli noise can be run independently from a tableau simulation, gonna implement this