🔧 Phase A: Add share_box() method to NyashBox trait and all Box implementations

Co-authored-by: moe-charm <217100418+moe-charm@users.noreply.github.com>

src/boxes/timer_box.rs

@@ -215,6 +215,12 @@ impl BoxCore for TimerBox {
 
 impl NyashBox for TimerBox {
     fn clone_box(&self) -> Box<dyn NyashBox> {
+    
+    /// 仮実装: clone_boxと同じ（後で修正）
+    fn share_box(&self) -> Box<dyn NyashBox> {
+        self.clone_box()
+    }
+
         Box::new(self.clone())
     }