Function sprs::prod::workspace_csr

pub fn workspace_csr<N, I, Mat1, Mat2>(_: &Mat1, rhs: &Mat2) -> Vec<N> where
    N: Copy + Num,
    I: SpIndex,
    Mat1: SpMatView<N, I>,
    Mat2: SpMatView<N, I>, 

Allocate the appropriate workspace for a CSR-CSR product