Function product_into 

pub(crate) fn product_into<L, R>(
    out: MatMut<'_, Complex>,
    left: MatRef<'_, L>,
    right: MatRef<'_, R>,
)
where
    L: Conjugate<Canonical = Complex>,
    R: Conjugate<Canonical = Complex>,

out = left right on the treams-rs pool (crate::threads::product). Pass .adjoint() views for conjugate-transposed factors; faer conjugates them inside the product kernel.