Use Bytes as the Container of ImageBuffer

Since we don't need to mutate images once loaded,
we avoid unnecessary extra allocations.

tiny_skia/src/raster.rs

@@ -83,7 +83,7 @@ impl Cache {
         let id = handle.id();
 
         if let hash_map::Entry::Vacant(entry) = self.entries.entry(id) {
-            let image = graphics::image::load(handle).ok()?.into_rgba8();
+            let image = graphics::image::load(handle).ok()?;
 
             let mut buffer =
                 vec![0u32; image.width() as usize * image.height() as usize];