Refactor timing tests to use mcrfpy.step() for synchronous execution

Converts tests from Timer-based async patterns to step()-based sync
patterns, eliminating timeout issues in headless testing.

Refactored tests:
- simple_timer_screenshot_test.py
- test_animation_callback_simple.py
- test_animation_property_locking.py
- test_animation_raii.py
- test_animation_removal.py
- test_timer_callback.py

Also updates KNOWN_ISSUES.md with comprehensive documentation on
the step()-based testing pattern including examples and best practices.

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

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

tests/unit/test_animation_callback_simple.py

@@ -1,73 +1,55 @@
 #!/usr/bin/env python3
-"""Simple test for animation callbacks - demonstrates basic usage"""
+"""Simple test for animation callbacks using mcrfpy.step() for synchronous execution"""
 
 import mcrfpy
 import sys
 
+print("Animation Callback Demo")
+print("=" * 30)
+
 # Global state to track callback
 callback_count = 0
-callback_demo = None  # Will be set in setup_and_run
 
 def my_callback(anim, target):
     """Simple callback that prints when animation completes"""
     global callback_count
     callback_count += 1
     print(f"Animation completed! Callback #{callback_count}")
-    # For now, anim and target are None - future enhancement
 
-def setup_and_run():
-    """Set up scene and run animation with callback"""
-    global callback_demo
-    # Create scene
-    callback_demo = mcrfpy.Scene("callback_demo")
-    callback_demo.activate()
+# Create scene
+callback_demo = mcrfpy.Scene("callback_demo")
+callback_demo.activate()
 
-    # Create a frame to animate
-    frame = mcrfpy.Frame((100, 100), (200, 200), fill_color=(255, 0, 0))
-    ui = callback_demo.children
-    ui.append(frame)
+# Create a frame to animate
+frame = mcrfpy.Frame((100, 100), (200, 200), fill_color=(255, 0, 0))
+ui = callback_demo.children
+ui.append(frame)
 
-    # Create animation with callback
-    print("Starting animation with callback...")
-    anim = mcrfpy.Animation("x", 400.0, 1.0, "easeInOutQuad", callback=my_callback)
-    anim.start(frame)
+# Test 1: Animation with callback
+print("Starting animation with callback (1.0s duration)...")
+anim = mcrfpy.Animation("x", 400.0, 1.0, "easeInOutQuad", callback=my_callback)
+anim.start(frame)
 
-    # Schedule check after animation should complete
-    mcrfpy.Timer("check", check_result, 1500, once=True)
+# Use mcrfpy.step() to advance past animation completion
+mcrfpy.step(1.5)  # Advance 1.5 seconds - animation completes at 1.0s
 
-def check_result(timer, runtime):
-    """Check if callback fired correctly"""
-    global callback_count, callback_demo
+if callback_count != 1:
+    print(f"FAIL: Expected 1 callback, got {callback_count}")
+    sys.exit(1)
+print("SUCCESS: Callback fired exactly once!")
 
-    if callback_count == 1:
-        print("SUCCESS: Callback fired exactly once!")
+# Test 2: Animation without callback
+print("\nTesting animation without callback (0.5s duration)...")
+anim2 = mcrfpy.Animation("y", 300.0, 0.5, "linear")
+anim2.start(frame)
 
-        # Test 2: Animation without callback
-        print("\nTesting animation without callback...")
-        ui = callback_demo.children
-        frame = ui[0]
+# Advance past second animation
+mcrfpy.step(0.7)
 
-        anim2 = mcrfpy.Animation("y", 300.0, 0.5, "linear")
-        anim2.start(frame)
+if callback_count != 1:
+    print(f"FAIL: Callback count changed to {callback_count}")
+    sys.exit(1)
 
-        mcrfpy.Timer("final", final_check, 700, once=True)
-    else:
-        print(f"FAIL: Expected 1 callback, got {callback_count}")
-        sys.exit(1)
-
-def final_check(timer, runtime):
-    """Final check - callback count should still be 1"""
-    global callback_count
-
-    if callback_count == 1:
-        print("SUCCESS: No unexpected callbacks fired!")
-        print("\nAnimation callback feature working correctly!")
-        sys.exit(0)
-    else:
-        print(f"FAIL: Callback count changed to {callback_count}")
-        sys.exit(1)
-
-# Start the demo
-print("Animation Callback Demo")
-print("=" * 30)
-setup_and_run()
+print("SUCCESS: No unexpected callbacks fired!")
+print("\nAnimation callback feature working correctly!")
+sys.exit(0)