Function expand_kv 

pub fn expand_kv(
    kv_c: &[f32],
    w_kv_b: &[f32],
    dims: DsaDims,
    seq: usize,
) -> (Vec<f32>, Vec<f32>)

2026-09-25: Expand the compressed latent into per-head K and V. NoPE only: it asserts qk_rope_head_dim == 0, so K is exactly qk_nope_head_dim wide.