Function pd_highlight_hunk 

#[unsafe(no_mangle)]
pub extern "C" fn pd_highlight_hunk(
    path_ptr: *const u8,
    path_len: u32,
    lines_ptr: *const u8,
    lines_len: u32,
) -> u64

Highlight a typed diff hunk with independent old/new lexer streams. lines is a JSON Line-union array; success has the same fallback shape as pd_highlight_lines.