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>

tests/unit/test_timer_once.py

@@ -1,6 +1,7 @@
 #!/usr/bin/env python3
 """
 Test once=True timer functionality
+Uses mcrfpy.step() to advance time in headless mode.
 """
 import mcrfpy
 import sys
@@ -18,20 +19,8 @@ def repeat_callback(timer, runtime):
     repeat_count += 1
     print(f"Repeat timer fired! Count: {repeat_count}, Timer.once: {timer.once}")
 
-def check_results(runtime):
-    print(f"\nFinal results:")
-    print(f"Once timer fired {once_count} times (expected: 1)")
-    print(f"Repeat timer fired {repeat_count} times (expected: 3+)")
-    
-    if once_count == 1 and repeat_count >= 3:
-        print("PASS: Once timer fired exactly once, repeat timer fired multiple times")
-        sys.exit(0)
-    else:
-        print("FAIL: Timer behavior incorrect")
-        sys.exit(1)
-
 # Set up the scene
-test_scene = mcrfpy.Scene("test_scene") 
+test_scene = mcrfpy.Scene("test_scene")
 test_scene.activate()
 
 # Create timers
@@ -43,5 +32,20 @@ print("\nCreating repeat timer with once=False (default)...")
 repeat_timer = mcrfpy.Timer("repeat_timer", repeat_callback, 100)
 print(f"Timer: {repeat_timer}, once={repeat_timer.once}")
 
-# Check results after 500ms
-mcrfpy.setTimer("check", check_results, 500)
+# Advance time using step() to let timers fire
+# Step 600ms total - once timer (100ms) fires once, repeat timer fires ~6 times
+print("\nAdvancing time with step()...")
+for i in range(6):
+    mcrfpy.step(0.1)  # 100ms each
+
+# Check results
+print(f"\nFinal results:")
+print(f"Once timer fired {once_count} times (expected: 1)")
+print(f"Repeat timer fired {repeat_count} times (expected: 3+)")
+
+if once_count == 1 and repeat_count >= 3:
+    print("PASS: Once timer fired exactly once, repeat timer fired multiple times")
+    sys.exit(0)
+else:
+    print("FAIL: Timer behavior incorrect")
+    sys.exit(1)