Function render_region_prepared_parallel 

pub fn render_region_prepared_parallel(
    list: &DisplayList,
    prepared: &PreparedDisplayList,
    vp_x: f64,
    vp_y: f64,
    vp_w: f64,
    vp_h: f64,
    pixel_w: u32,
    pixel_h: u32,
    dpi: f64,
    icc: Option<&IccCache>,
    image_cache: Option<&ImageCache>,
    no_aa: bool,
) -> Vec<u8> 

Render a viewport region using parallel banded rendering via rayon.

This is the WASM counterpart to the parallel path in render_banded_to_sink. All bands are rendered in parallel using par_iter, then assembled into the final RGBA buffer in order.

Requires the parallel feature (rayon). Falls back to sequential rendering if parallel is not enabled.