Function inner_product_f16 

pub fn inner_product_f16<Idx: Copy + Ord>(
    x_idx: &[Idx],
    x_val: &[Half],
    y_idx: &[Idx],
    y_val: &[Half],
) -> Result<f32, LengthMismatch>

Σ x·y over matching indices for f16 operands; a disjoint-range fast-out skips widening when the operands cannot intersect.