Fix UIFrame RenderTexture positioning and toggling issues

- Fix #223: Use `position` instead of `box.getPosition()` for render_sprite
  positioning. The box was being set to (0,0) for texture rendering and
  never restored, causing frames to render at wrong positions.

- Fix #224: Add disableRenderTexture() method and call it when toggling
  clip_children or cache_subtree off. This properly cleans up the texture
  and prevents stale rendering.

- Fix #225: Improve dirty propagation in markContentDirty() to propagate
  to parent even when already dirty, if the parent was cleared (rendered)
  since last propagation. Prevents child changes from being invisible.

- Fix #226: Add fallback to standard rendering when RenderTexture can't
  be created (e.g., zero-size frame). Prevents inconsistent state.

Closes #223, closes #224, closes #225, closes #226

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/regression/issue_223_clip_children_test.py

@@ -0,0 +1,95 @@
+"""Test clip_children positioning and toggling fixes (#223, #224, #225, #226)
+
+Issue #223: Frame appears at wrong position with clip_children
+Issue #224: Stale rendering after toggling clip_children off
+Issue #225: Child changes don't update parent's cached texture
+Issue #226: Zero-size frame with clip_children causes inconsistent state
+
+This test verifies the property/positioning behavior. Visual rendering verification
+requires a game loop and should be done with the demo system.
+"""
+import mcrfpy
+import sys
+
+errors = []
+
+# Test 1: Position with clip_children=True (#223)
+frame = mcrfpy.Frame(pos=(100, 100), size=(200, 200), clip_children=True)
+if frame.x != 100:
+    errors.append(f"#223 Test 1: Expected x=100, got {frame.x}")
+if frame.y != 100:
+    errors.append(f"#223 Test 1: Expected y=100, got {frame.y}")
+
+# Add a child
+child = mcrfpy.Caption(text="Hello", pos=(10, 10))
+frame.children.append(child)
+
+# Test 2: Toggle clip_children off (#224)
+frame.clip_children = False
+if frame.x != 100:
+    errors.append(f"#224 Test 2 after toggle off: Expected x=100, got {frame.x}")
+if frame.y != 100:
+    errors.append(f"#224 Test 2 after toggle off: Expected y=100, got {frame.y}")
+
+# Toggle back on
+frame.clip_children = True
+if frame.x != 100:
+    errors.append(f"#224 Test 2 after toggle on: Expected x=100, got {frame.x}")
+
+# Test 3: Zero-size frame with clip_children (#226)
+zero_frame = mcrfpy.Frame(pos=(50, 50), size=(0, 0), clip_children=True)
+if zero_frame.x != 50:
+    errors.append(f"#226 Test 3: Expected x=50, got {zero_frame.x}")
+if zero_frame.y != 50:
+    errors.append(f"#226 Test 3: Expected y=50, got {zero_frame.y}")
+
+# Test 4: cache_subtree toggle similar to clip_children
+cache_frame = mcrfpy.Frame(pos=(200, 200), size=(100, 100), cache_subtree=True)
+if cache_frame.x != 200:
+    errors.append(f"Test 4: Expected x=200, got {cache_frame.x}")
+
+cache_frame.cache_subtree = False
+if cache_frame.x != 200:
+    errors.append(f"Test 4 after toggle: Expected x=200, got {cache_frame.x}")
+
+# Test 5: Both clip_children and cache_subtree
+both_frame = mcrfpy.Frame(pos=(300, 300), size=(100, 100), clip_children=True, cache_subtree=True)
+
+# Turn off clip_children (cache_subtree should keep texture active)
+both_frame.clip_children = False
+if both_frame.x != 300:
+    errors.append(f"Test 5 after clip toggle: Expected x=300, got {both_frame.x}")
+
+# Turn off cache_subtree too
+both_frame.cache_subtree = False
+if both_frame.x != 300:
+    errors.append(f"Test 5 after full toggle: Expected x=300, got {both_frame.x}")
+
+# Test 6: Moving a frame with clip_children
+frame.x = 150
+frame.y = 150
+if frame.x != 150:
+    errors.append(f"Test 6: Expected x=150, got {frame.x}")
+if frame.y != 150:
+    errors.append(f"Test 6: Expected y=150, got {frame.y}")
+
+# Test 7: Child modification (dirty propagation #225)
+# This tests that modifying a child marks the parent dirty
+# We can't directly test render_dirty flag from Python, but we can verify
+# that the API doesn't crash and positions stay correct
+frame2 = mcrfpy.Frame(pos=(400, 400), size=(100, 100), clip_children=True)
+child2 = mcrfpy.Caption(text="Test", pos=(5, 5))
+frame2.children.append(child2)
+
+# Modify child text
+child2.text = "Changed"
+if frame2.x != 400:
+    errors.append(f"Test 7: Expected x=400 after child change, got {frame2.x}")
+
+# Report results
+if errors:
+    print("FAIL: " + "; ".join(errors))
+    sys.exit(1)
+else:
+    print("PASS: clip_children positioning and toggling tests")
+    sys.exit(0)