refactor: use effect for assignSelector in BaseGameClient

Replace subscribe with effect in assignSelector to ensure the
selector value is tracked and the callback is executed within
the reactive context.

src/core/game-client.ts

@@ -60,7 +60,9 @@ export abstract class BaseGameClient<
 
   assignSelector<S>(selector: (t: T) => S, callback: (s: S) => void) {
     const selected = computed(() => selector(this._context.value));
-    return selected.subscribe(callback);
+    return effect(() => {
+      callback(selected.value);
+    });
   }
 
   addInterruption() {