Function argsort 

pub fn argsort<T, D>(
    a: &Array<T, D>,
    axis: Option<usize>,
) -> FerrayResult<Array<u64, IxDyn>>
where
    T: Element + PartialOrd + Copy,
    D: Dimension,

Return the indices that would sort an array along the given axis.

When axis is None, the array is flattened before computing indices and a 1-D array is returned (matching NumPy behaviour).

Returns u64 indices.

Equivalent to numpy.argsort.