PauliString.before/after take measurement indices

[mmcewen-g]

Currently PauliString.before and PauliString.after are only implemented for measurement-less circuits

It would be nice to add another overload letting us provide it with appropriate measurement indices, so we can project pauli strings through QEC circuits
e.g.
stim.PauliString("ZZ").after(stim.Circuit("M 0"), measurement_indices=[-1]) == stim.PauliString("_Z")