refactor: split kra (krita) logic into image hook

may further split this into its own crate;
seems quite useful! (albeit somewhat short and easy)

since there aren't any runtime dependancies,
it could even go into image-extras maybe

src/main.rs

@@ -7,6 +7,7 @@ use iced::{
 };
 use image::{EncodableLayout, RgbaImage, imageops};
 
+mod kra;
 mod utils;
 
 #[derive(Clone, Debug)]
@@ -209,6 +210,7 @@ impl State {
 
 fn main() -> Result<(), iced::Error> {
     jxl_oxide::integration::register_image_decoding_hook();
+    kra::register();
 
     iced::application(State::new, State::update, State::view)
         .subscription(State::subscription)