Refactor 11 more tests to mcrfpy.step() pattern

Converted from Timer-based async to step()-based sync:
- test_simple_callback.py
- test_empty_animation_manager.py
- test_frame_clipping.py
- test_frame_clipping_advanced.py
- test_grid_children.py
- test_color_helpers.py
- test_no_arg_constructors.py
- test_properties_quick.py
- test_simple_drawable.py
- test_python_object_cache.py
- WORKING_automation_test_example.py

Only 4 tests remain with Timer-based patterns (2 are headless detection
tests that may require special handling).

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

Co-Authored-By: Frack <frack@goblincorps.dev>
Co-Authored-By: Claude <noreply@anthropic.com>

tests/unit/test_simple_callback.py

@@ -1,14 +1,32 @@
 #!/usr/bin/env python3
-"""Very simple callback test"""
+"""Very simple callback test - refactored to use mcrfpy.step()"""
 import mcrfpy
 import sys
 
+callback_fired = False
+
 def cb(a, t):
+    global callback_fired
+    callback_fired = True
     print("CB")
 
+# Setup scene
 test = mcrfpy.Scene("test")
 test.activate()
+mcrfpy.step(0.01)  # Initialize
+
+# Create entity and animation
 e = mcrfpy.Entity((0, 0), texture=None, sprite_index=0)
 a = mcrfpy.Animation("x", 1.0, 0.1, "linear", callback=cb)
 a.start(e)
-mcrfpy.Timer("exit", lambda t, r: sys.exit(0), 200, once=True)
+
+# Advance past animation duration (0.1s)
+mcrfpy.step(0.15)
+
+# Verify callback fired
+if callback_fired:
+    print("PASS: Callback fired")
+    sys.exit(0)
+else:
+    print("FAIL: Callback did not fire")
+    sys.exit(1)