Function decode_coding_tree 

pub fn decode_coding_tree(
    x: usize,
    y: usize,
    log2_cu_size: u8,
    depth: u8,
    max_depth: u8,
    qp: i8,
    pic_width: usize,
    pic_height: usize,
    results: &mut Vec<DecodedCu>,
)

Recursively decode a coding tree (quad-tree split).

depth starts at 0 for the CTU root. max_depth is derived from SPS (log2_diff_max_min_cb_size). When depth == max_depth or the split flag is 0, the node is a leaf CU.

This is a framework function; actual CABAC parsing is not implemented. Instead, it treats each leaf CU as intra-DC predicted with zero residual.