[FEATURE] `mx.repeat` with variable number of repetitions

[kyrollosyanny]

Describe the bug
In numpy, np.repeat can accept both int and array type for the repetition. The main use case for passing an array is if each element in the original array needs to repeated a different number of times. Currently, this fails in MLX.

To Reproduce
In numpy:

a=np.array([1,2,3,4])

print(np.repeat(a,a))

[1 2 2 3 3 3 4 4 4 4]

in MlX, this does not work since repetition needs to be an integer.

It would be great if we can add this behavior to mx.repeat unless there is another efficient way to do this.

Thanks