Function c_decode_vector_block 

pub fn c_decode_vector_block(
    indices: &[u16],
    codebook: &[f32],
    codebook_size: usize,
    block_dim: usize,
) -> Vec<f32>

Decode a vector block: gather codewords by index.

Panics

Panics if any index >= codebook_size (caller should validate).