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/simple_timer_screenshot_test.py

@@ -1,28 +1,23 @@
 #!/usr/bin/env python3
-"""Simplified test to verify timer-based screenshots work"""
+"""Test to verify timer-based screenshots work using mcrfpy.step() for synchronous execution"""
 import mcrfpy
 from mcrfpy import automation
+import sys
 
 # Counter to track timer calls
 call_count = 0
 
-def take_screenshot_and_exit(timer, runtime):
-    """Timer callback that takes screenshot then exits"""
+def take_screenshot(timer, runtime):
+    """Timer callback that takes screenshot"""
     global call_count
     call_count += 1
-
-    print(f"\nTimer callback fired! (call #{call_count})")
+    print(f"Timer callback fired! (call #{call_count}, runtime={runtime})")
 
     # Take screenshot
     filename = f"timer_screenshot_test_{call_count}.png"
     result = automation.screenshot(filename)
     print(f"Screenshot result: {result} -> {filename}")
 
-    # Exit after first call
-    if call_count >= 1:
-        print("Exiting game...")
-        mcrfpy.exit()
-
 # Set up a simple scene
 print("Creating test scene...")
 test = mcrfpy.Scene("test")
@@ -35,6 +30,17 @@ frame = mcrfpy.Frame(pos=(100, 100), size=(200, 200),
 ui.append(frame)
 
 print("Setting timer to fire in 100ms...")
-mcrfpy.Timer("screenshot_timer", take_screenshot_and_exit, 100, once=True)
+timer = mcrfpy.Timer("screenshot_timer", take_screenshot, 100, once=True)
+print(f"Timer created: {timer}")
 
-print("Setup complete. Game loop starting...")
+# Use mcrfpy.step() to advance simulation synchronously instead of waiting
+print("Advancing simulation by 200ms using step()...")
+mcrfpy.step(0.2)  # Advance 200ms - timer at 100ms should fire
+
+# Verify timer fired
+if call_count >= 1:
+    print("SUCCESS: Timer fired and screenshot taken!")
+    sys.exit(0)
+else:
+    print(f"FAIL: Expected call_count >= 1, got {call_count}")
+    sys.exit(1)