Function dequantize_vec 

pub fn dequantize_vec(
    config: &TurboQuantConfig,
    block: &PackedBlock,
) -> Result<Vec<f32>>

Dequantizes a PackedBlock back into a floating-point vector.

Integration: unpacks indices, looks up centroids, applies inverse rotation, and scales by the stored norm.

Errors

Returns an error if the inverse rotation fails (should not happen if the block was produced by quantize_vec with valid config).