Timer refactor: stopwatch-like semantics, mcrfpy.timers collection closes #173

Major Timer API improvements:
- Add `stopped` flag to Timer C++ class for proper state management
- Add `start()` method to restart stopped timers (preserves callback)
- Add `stop()` method that removes from engine but preserves callback
- Make `active` property read-write (True=start/resume, False=pause)
- Add `start=True` init parameter to create timers in stopped state
- Add `mcrfpy.timers` module-level collection (tuple of active timers)
- One-shot timers now set stopped=true instead of clearing callback
- Remove deprecated `setTimer()` and `delTimer()` module functions

Timer callbacks now receive (timer, runtime) instead of just (runtime).
Updated all tests to use new Timer API and callback signature.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/McRFPy_API.h

@@ -43,9 +43,7 @@ public:
     // Internal - used by PySceneObject::activate()
     static PyObject* _setScene(PyObject*, PyObject*);
 
-    // timer control
-    static PyObject* _setTimer(PyObject*, PyObject*);
-    static PyObject* _delTimer(PyObject*, PyObject*);
+    // Note: setTimer/delTimer removed in #173 - use Timer objects instead
 
     // #153 - Headless simulation control
     static PyObject* _step(PyObject*, PyObject*);
@@ -88,6 +86,9 @@ public:
     static int api_set_current_scene(PyObject* value);
     static PyObject* api_get_scenes();
 
+    // #173: Module-level timer collection accessor
+    static PyObject* api_get_timers();
+
     // Exception handling - signal game loop to exit on unhandled Python exceptions
     static std::atomic<bool> exception_occurred;
     static std::atomic<int> exit_code;