Modernize Crypt of Sokoban demo game and fix timer segfault

Game script updates (src/scripts/):
- Migrate Sound/Music API: createSoundBuffer() -> Sound() objects
- Migrate Scene API: sceneUI("name") -> scene.children
- Migrate Timer API: setTimer/delTimer -> Timer objects with stop()
- Fix callback signatures: (x,y,btn,event) -> (pos,btn,action) with Vector
- Fix grid_size unpacking: now returns Vector, use .x/.y with int()

Segfault fix (src/PyTimer.cpp):
- Remove direct map erase in PyTimer::stop() that caused iterator
  invalidation when timer.stop() was called from within a callback
- Now just marks timer as stopped; testTimers() handles safe removal

The game now starts and runs without crashes.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/PyTimer.cpp

@@ -156,14 +156,10 @@ PyObject* PyTimer::stop(PyTimerObject* self, PyObject* Py_UNUSED(ignored)) {
         return nullptr;
     }
 
-    // Remove from game engine map (but preserve the Timer data!)
-    if (Resources::game && !self->name.empty()) {
-        auto it = Resources::game->timers.find(self->name);
-        if (it != Resources::game->timers.end() && it->second == self->data) {
-            Resources::game->timers.erase(it);
-        }
-    }
-
+    // Just mark as stopped - do NOT erase from map here!
+    // Removing from the map during iteration (e.g., from a timer callback)
+    // would invalidate iterators in testTimers(). The stopped flag tells
+    // testTimers() to safely remove this timer on its next pass.
     self->data->stop();
     // NOTE: We do NOT reset self->data here - the timer can be restarted
     Py_RETURN_NONE;