Function build_v_with_mimo 

pub fn build_v_with_mimo<const D: usize, const DP1: usize>(
    x: Tensor<D>,
    mimo_x_hmp: Option<&Tensor<3>>,
    insert_dim: usize,
) -> Tensor<DP1>

Build the MIMO value tensor v = x ⊙ mimo_x with broadcasting.

Inserts a mimo_rank axis at insert_dim. When mimo_x_hmp is None (SISO), the inserted axis has size 1 and x is passed through; otherwise broadcasting fills the inserted axis to size mimo_rank.

DP1 = D + 1.