Upgrade AVIF decoding code

- Update to newer APIs.
 - Avoid manual pixel-by-pixel copy in favour of decoding directly to desired format & bit depth.
 - Avoid use-after-free by cloning the Uint8Array Wasm memory view into a JS-owned Uint8Array right away.

src/codecs/avif/decoder.ts

@@ -15,6 +15,5 @@ export async function decode(data: ArrayBuffer): Promise<ImageData> {
     rawImage.height,
   );
 
-  module.free_result();
   return result;
 }