Function stack_blur_rgba32 

pub fn stack_blur_rgba32(rbuf: &mut RowAccessor, rx: u32, ry: u32)

Apply stack blur to an RGBA32 rendering buffer.

Port of C++ stack_blur_rgba32<Img>. Operates in-place on the buffer with independent horizontal and vertical radii. Radius is clamped to 254.

Component order: R=0, G=1, B=2, A=3.