Function project_kv_block_ref 

pub fn project_kv_block_ref(
    k_block: &[bf16],
    p: &[bf16],
    block_size: usize,
    num_kv_heads: usize,
    head_dim: usize,
    r: usize,
) -> Vec<bf16>

2026-09-25: Project every token of one block; output [num_kv_heads, block_size, r].