Add support for repeat

[davidmascharka]

Useful for nearest interpolation, for example:

>>> np.arange(4).reshape(2, 2).repeat(2, axis=0).repeat(2, axis=1)
array([[0, 0, 1, 1],
       [0, 0, 1, 1],
       [2, 2, 3, 3],
       [2, 2, 3, 3]])

[rsokl]

This would be great to have. What is super neat is that I think sliding_window_view basically does all of the heavy-lifting here for the backprop logic:

• repeat-size = window-size + step-size
• sum over the windows

The fact that axis can only be an int makes it almost too-easy. We could totally have handled tuples of axes too 💪

[rsokl]

Yep! Given

x = np.arange(4).reshape(2, 2).repeat(2, axis=0)

Accumulating the grad in backprop would be:

sliding_window_view(grad, window_shape=(2, 1), step=(2, 1)).sum(axis=(-2, -1))

😎