refactor: try to integrate jpegxl_rs with hooks

The problem is, libjxl_rs does not offer a way to get metadata
before decoding the entire image.

As such, there is no reasonable way to implement ImageDecoder here;
I think it's possible to make it decode the image on init,
but that would lead to unexpected behavior performance-wise.

src/jxl.rs

@@ -0,0 +1,22 @@
+pub struct JxlDecoder<'a> {
+    metadata: jpegxl_rs::decode::Metadata,
+    inner: jpegxl_rs::decode::JxlDecoder<'a, 'a>,
+}
+
+impl<'a> image::ImageDecoder for JxlDecoder<'a> {
+    fn color_type(&self) -> image::ColorType {
+        image::ColorType::Rgba8
+    }
+    fn icc_profile(&mut self) -> image::ImageResult<Option<Vec<u8>>> {
+        Ok(self.metadata.icc_profile.clone())
+    }
+    fn dimensions(&self) -> (u32, u32) {}
+    fn read_image(self, buf: &mut [u8]) -> image::ImageResult<()>
+    where
+        Self: Sized,
+    {
+    }
+    fn read_image_boxed(self: Box<Self>, buf: &mut [u8]) -> image::ImageResult<()> {
+        self.read_image(buf)
+    }
+}

src/main.rs

@@ -7,6 +7,7 @@ use iced::{
 };
 use image::{EncodableLayout, RgbaImage, imageops};
 
+mod jxl;
 mod utils;
 
 #[derive(Clone, Debug)]