Function parse_transform_unit 

pub fn parse_transform_unit(
    state: &mut HevcSliceCabacState<'_>,
    log2_tu_size: u32,
    is_luma: bool,
    sign_data_hiding_enabled: bool,
) -> Vec<i16>

Parse a transform unit’s residual coefficients.

Implements the coefficient coding syntax from ITU-T H.265 section 7.3.8.12 including last-significant-coefficient position, sub-block significance flags, per-coefficient significance, greater-than-1/2 flags, and bypass- coded sign/remaining-level.

Returns the dequantised coefficient array in raster order (row-major), with length (1 << log2_tu_size)^2.