Function process_offset_pixel 

fn process_offset_pixel(
    pixmap: &mut Pixmap,
    x: u16,
    y: u16,
    dx_pixels: i32,
    dy_pixels: i32,
    width: u16,
    height: u16,
    transparent: PremulRgba8,
)

Process a single pixel during offset operation.

This moves the pixel to its new position (if in bounds) and clears the source position if it’s in the exposed region.