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_removal.py

@@ -1,40 +1,14 @@
 #!/usr/bin/env python3
 """
-Test if the crash is related to removing animated objects
+Test if the crash is related to removing animated objects.
+Uses mcrfpy.step() for synchronous test execution.
 """
 
 import mcrfpy
 import sys
 
-def clear_and_recreate(timer, runtime):
-    """Clear UI and recreate - mimics demo switching"""
-    print(f"\nTimer called at {runtime}")
-    
-    ui = test.children
-    
-    # Remove all but first 2 items (like clear_demo_objects)
-    print(f"Scene has {len(ui)} elements before clearing")
-    while len(ui) > 2:
-        ui.remove(len(ui)-1)
-    print(f"Scene has {len(ui)} elements after clearing")
-    
-    # Create new animated objects
-    print("Creating new animated objects...")
-    for i in range(5):
-        f = mcrfpy.Frame(100 + i*50, 200, 40, 40)
-        f.fill_color = mcrfpy.Color(100 + i*30, 50, 200)
-        ui.append(f)
-        
-        # Start animation on the new frame
-        target_x = 300 + i * 50
-        anim = mcrfpy.Animation("x", float(target_x), 1.0, "easeInOut")
-        anim.start(f)
-    
-    print("New objects created and animated")
-
-    # Schedule exit
-    global exit_timer
-    exit_timer = mcrfpy.Timer("exit", lambda t, r: sys.exit(0), 2000, once=True)
+print("Animation Removal Test")
+print("=" * 40)
 
 # Create initial scene
 print("Creating scene...")
@@ -47,20 +21,61 @@ title = mcrfpy.Caption(pos=(400, 20), text="Test Title")
 subtitle = mcrfpy.Caption(pos=(400, 50), text="Test Subtitle")
 ui.extend([title, subtitle])
 
+# Initialize scene
+mcrfpy.step(0.1)
+
 # Create initial animated objects
 print("Creating initial animated objects...")
+initial_frames = []
 for i in range(10):
     f = mcrfpy.Frame(pos=(50 + i*30, 100), size=(25, 25))
     f.fill_color = mcrfpy.Color(255, 100, 100)
     ui.append(f)
-    
+    initial_frames.append(f)
+
     # Animate them
     anim = mcrfpy.Animation("y", 300.0, 2.0, "easeOutBounce")
     anim.start(f)
 
 print(f"Initial scene has {len(ui)} elements")
 
-# Schedule the clear and recreate
-switch_timer = mcrfpy.Timer("switch", clear_and_recreate, 1000, once=True)
+# Let animations run a bit
+mcrfpy.step(0.5)
 
-print("\nEntering game loop...")
+# Clear and recreate - mimics demo switching
+print("\nClearing and recreating...")
+print(f"Scene has {len(ui)} elements before clearing")
+
+# Remove all but first 2 items (like clear_demo_objects)
+# Use reverse iteration to remove by element
+while len(ui) > 2:
+    ui.remove(ui[-1])
+
+print(f"Scene has {len(ui)} elements after clearing")
+
+# Create new animated objects
+print("Creating new animated objects...")
+for i in range(5):
+    f = mcrfpy.Frame(pos=(100 + i*50, 200), size=(40, 40))
+    f.fill_color = mcrfpy.Color(100 + i*30, 50, 200)
+    ui.append(f)
+
+    # Start animation on the new frame
+    target_x = 300 + i * 50
+    anim = mcrfpy.Animation("x", float(target_x), 1.0, "easeInOut")
+    anim.start(f)
+
+print("New objects created and animated")
+print(f"Scene now has {len(ui)} elements")
+
+# Let new animations run
+mcrfpy.step(1.5)
+
+# Final check
+print(f"\nFinal scene has {len(ui)} elements")
+if len(ui) == 7:  # 2 captions + 5 new frames
+    print("SUCCESS: Animation removal test passed!")
+    sys.exit(0)
+else:
+    print(f"FAIL: Expected 7 elements, got {len(ui)}")
+    sys.exit(1)