add the shape label like in python.

[demhademha]

The Python API can be used both ways:

mx.random.uniform(0, 1, (3, 3))
mx.random.uniform(0, 1, shape=(3, 3))

we should add the shape label for consistancy and clarity.

[davidkoski]

The Swift API consistently (I think) omits the shape label everywhere when shape is required. In general python allows labels for everything but can omit them if they are not required (it is basically a dictionary of args) so this isn't something we can do in swift.