Add _repr_pretty_ to all results and devices classes

[Strilanc]

This method is used preferentially over repr in Jupyter notebooks and in ipython:

In [1]: class C:
   ...:     def __str__(self):
   ...:         return 'str'
   ...:     def __repr__(self):
   ...:         return 'repr'
   ...:     def _repr_pretty_(self, p, cycle):
   ...:         p.text('pretty')
   ...:     

In [2]: C()
Out[2]: pretty

repr is supposed to be unambiguous, so we often can't be too creative with it. In order to make the ipython experience smoother we should show coarser easier to read information.

Circuit works the way it should (pretty printing a circuit), but e.g. TrialResult does not. Support is generally very easy, because our __str__ methods do the hard lifting:

    def _repr_pretty_(self, p: Any, cycle: bool) -> None:
        """Shown in ipython and Jupyter notebooks."""
        if cycle:
            p.text('TrialResult(...)')
        else:
            p.text(self.__str__())

[dabacon]

We don't have many implementations of this. It is probably most urgent for "heavy" objects since otherwise it uses repr.

[dabacon]

Here is a pass on object we should consider making sure we have this for

cirq.Device
cirq.CliffordTrialResult
cirq.DensityMatrixStepResult
cirq.SimulationTrialResult
cirq.WaveFunctionStepResult
cirq.WaveFunctionTrialResult
cirq.IonDevice
cirq.google.Sycamore
cirq.google.Sycamore23

Some of these may already be done or covered by superclasses.

[dabacon]

I guess we also have guidance to use repr_pretty for Gates. So we should do a complete audit.

[dabacon]

There are now on results and on devices.