Function generic_batched_columnwise_dot_product 

pub fn generic_batched_columnwise_dot_product<F, EF, R, I, const N: usize>(
    acc: &mut [EF::ExtensionPacking],
    items: I,
)
where
    F: Field,
    EF: ExtensionField<F>,
    R: Iterator<Item = F::Packing>,
    I: Iterator<Item = (R, [EF; N])>,

The generic accumulation behind Field::batched_columnwise_dot_product: acc[c * N + j] += scales[j] * row[c] over a stream of packed rows.

Kept as a free function so that specialized Field implementations can fall back to it for extension degrees their kernels do not cover.