fix event typing

You need to type it like CustomEvent<...> because when forwarding events it could also be MouseEvent or sth like that

src/runtime/internal/Component.ts

@@ -224,7 +224,7 @@ export class SvelteComponent<
 		this.$destroy = noop;
 	}
 
-	$on<K extends Extract<keyof Events, string>>(type: K, callback: (e: CustomEvent<Events[K]>) => void) {
+	$on<K extends Extract<keyof Events, string>>(type: K, callback: (e: Events[K]) => void) {
 		const callbacks = (this.$$.callbacks[type] || (this.$$.callbacks[type] = []));
 		callbacks.push(callback);
 

src/runtime/internal/dev.ts

@@ -103,7 +103,7 @@ export interface SvelteComponentDev<
 	Slots extends Record<string, any> = any
 > {
 	$set(props?: Partial<Props> & Record<string, any>): void;
-	$on<K extends Extract<keyof Events, string>>(type: K, callback: (e: CustomEvent<Events[K]>) => void): () => void;
+	$on<K extends Extract<keyof Events, string>>(type: K, callback: (e: Events[K]) => void): () => void;
 	$destroy(): void;
 	[accessor: string]: any;
 }