Function quantize_codeblock_subband 

pub fn quantize_codeblock_subband(
    coefficients: &[f64],
    width: usize,
    height: usize,
    sub_band_type: J2kSubBandType,
    options: Htj2k97CodeBlockOptions,
) -> PrequantizedHtj2k97Subband

Quantize a single float subband and slice it into code-block-major layout.

Code-blocks are emitted outer cby, inner cbx; each block’s coefficients are row-major, matching the native encoder’s copy_code_block_coefficients.