Function source_over 

pub fn source_over(src: U8x4Rgba, dst: U8x4Rgba) -> U8x4Rgba

Blends src over dst using the Porter-Duff SRC_OVER operator for straight-alpha pixels: out = src + dst * (1 - src.a) for each channel, including alpha.

Delegates to the alpha-blend crate’s BlendMode::SourceOver, converting through F32x4Rgba for the blend math.