• Use webpmux if available to unpack and repack animated webp images.
• Fix Animated WebP images:
  • Sometimes being repacked in reverse frame order.
  • Sometimes degrading quality.
  • Sometimes dropping frames.
• Use secure python temporary directory for unpacking animated webp images and
  chaining webp conversion input.
• Use img2webp if available for animated conversion to webp from png.
• Use memory buffers instead of disk for webp output.