Function afarray::reduce_sum

pub fn reduce_sum<'a, E, S>(
    blocks: S, 
    dtype: NumberType, 
    block_size: usize, 
    stride: u64
) -> Box<dyn Stream<Item = Result<Array, E>> + Send + Unpin + 'a> where
    E: Send + 'a,
    S: Stream<Item = Result<Array, E>> + Send + Unpin + 'a, 

Compute the sum of each stride of a [Stream] of Arrays.