Cast GWLP_USERDATA to ShortcutManagerImpl

Use the concrete ShortcutManagerImpl type when retrieving the pointer from GWLP_USERDATA in the window procedure. This replaces the previous reinterpret_cast to an ambiguous Impl type and wraps the long cast onto a new line for readability and to avoid potential type/name errors.

Author: lijy91

src/platform/windows/shortcut_manager_windows.cpp

@@ -223,7 +223,8 @@ class ShortcutManagerImpl final : public ShortcutManager::Impl {
       return DefWindowProc(hwnd, msg, wparam, lparam);
     }
 
-    auto* self = reinterpret_cast<Impl*>(GetWindowLongPtr(hwnd, GWLP_USERDATA));
+    auto* self =
+        reinterpret_cast<ShortcutManagerImpl*>(GetWindowLongPtr(hwnd, GWLP_USERDATA));
     if (!self) {
       return DefWindowProc(hwnd, msg, wparam, lparam);
     }