This MR:

• Checks if the dimensions of the image are the same as the dimensions of the page for image extraction using pikepdf.
• Adds some extra documentation for extract_image_pike
• Adds tests for the image extraction using pikepdf

When comparing dimensions we only check if the aspect ratio is the same, since that is the only information that is available in the embedded image object. The real size on the page depends on the draw instruction that is not easily available to pikepdf as far as I know.