API: require __array__ in EA interface

[jbrockmendel]

Confusion on this point has come up a couple times, in part because np.asarray(self) is called in several of the base class methods.

We should also require that np.asarray(self) match self.to_numpy() i.e. when no args/kwargs are specified.

[prakhar987]

Do we want to add __array__ to the base class and use this method instead of directly calling np.asarray(self) ?

For making sure the behaviour matches self.to_numpy() I can add some tests as well.

[prakhar987]

take

[jbrockmendel]

@prakhar987 lets hold off on this and make sure there is consensus first.