feat(rendering): implement RenderTexture base infrastructure and UIFrame clipping (#6)

- Added RenderTexture support to UIDrawable base class
  - std::unique_ptr<sf::RenderTexture> for opt-in rendering
  - Dirty flag system for optimization
  - enableRenderTexture() and markDirty() methods

- Implemented clip_children property for UIFrame
  - Python-accessible boolean property
  - Automatic RenderTexture creation when enabled
  - Proper coordinate transformation for nested frames

- Updated UIFrame::render() for clipping support
  - Renders to RenderTexture when clip_children=true
  - Handles nested clipping correctly
  - Only re-renders when dirty flag is set

- Added comprehensive dirty flag propagation
  - All property setters mark frame as dirty
  - Size changes recreate RenderTexture
  - Animation system integration

- Created tests for clipping functionality
  - Basic clipping test with visual verification
  - Advanced nested clipping test
  - Dynamic resize handling test

This is Phase 1 of the RenderTexture overhaul, providing the foundation
for advanced rendering effects like blur, glow, and viewport rendering.

tests/test_frame_clipping_advanced.py

@@ -0,0 +1,103 @@
+#!/usr/bin/env python3
+"""Advanced test for UIFrame clipping with nested frames"""
+
+import mcrfpy
+from mcrfpy import Color, Frame, Caption, Vector
+import sys
+
+def test_nested_clipping(runtime):
+    """Test nested frames with clipping"""
+    mcrfpy.delTimer("test_nested_clipping")
+    
+    print("Testing advanced UIFrame clipping with nested frames...")
+    
+    # Create test scene
+    scene = mcrfpy.sceneUI("test")
+    
+    # Create outer frame with clipping enabled
+    outer = Frame(50, 50, 400, 300,
+                  fill_color=Color(50, 50, 150),
+                  outline_color=Color(255, 255, 255),
+                  outline=3)
+    outer.name = "outer"
+    outer.clip_children = True
+    scene.append(outer)
+    
+    # Create inner frame that extends beyond outer bounds
+    inner = Frame(200, 150, 300, 200,
+                  fill_color=Color(150, 50, 50),
+                  outline_color=Color(255, 255, 0),
+                  outline=2)
+    inner.name = "inner"
+    inner.clip_children = True  # Also enable clipping on inner frame
+    outer.children.append(inner)
+    
+    # Add content to inner frame that extends beyond its bounds
+    for i in range(5):
+        caption = Caption(10, 30 * i, f"Line {i+1}: This text should be double-clipped")
+        caption.font_size = 14
+        caption.fill_color = Color(255, 255, 255)
+        inner.children.append(caption)
+    
+    # Add a child frame to inner that extends way out
+    deeply_nested = Frame(250, 100, 200, 150,
+                         fill_color=Color(50, 150, 50),
+                         outline_color=Color(255, 0, 255),
+                         outline=2)
+    deeply_nested.name = "deeply_nested"
+    inner.children.append(deeply_nested)
+    
+    # Add status text
+    status = Caption(50, 380, 
+                    "Nested clipping test:\n"
+                    "- Blue outer frame clips red inner frame\n"
+                    "- Red inner frame clips green deeply nested frame\n"
+                    "- All text should be clipped to frame bounds")
+    status.font_size = 12
+    status.fill_color = Color(200, 200, 200)
+    scene.append(status)
+    
+    # Test render texture size handling
+    print(f"Outer frame size: {outer.w}x{outer.h}")
+    print(f"Inner frame size: {inner.w}x{inner.h}")
+    
+    # Dynamically resize frames to test RenderTexture recreation
+    def resize_test(runtime):
+        mcrfpy.delTimer("resize_test")
+        print("Resizing frames to test RenderTexture recreation...")
+        outer.w = 450
+        outer.h = 350
+        inner.w = 350
+        inner.h = 250
+        print(f"New outer frame size: {outer.w}x{outer.h}")
+        print(f"New inner frame size: {inner.w}x{inner.h}")
+        
+        # Take screenshot after resize
+        mcrfpy.setTimer("screenshot_resize", take_resize_screenshot, 500)
+    
+    def take_resize_screenshot(runtime):
+        mcrfpy.delTimer("screenshot_resize")
+        from mcrfpy import automation
+        automation.screenshot("frame_clipping_resized.png")
+        print("\nAdvanced test completed!")
+        print("Screenshots saved:")
+        print("  - frame_clipping_resized.png (after resize)")
+        sys.exit(0)
+    
+    # Take initial screenshot
+    from mcrfpy import automation
+    automation.screenshot("frame_clipping_nested.png")
+    print("Initial screenshot saved: frame_clipping_nested.png")
+    
+    # Schedule resize test
+    mcrfpy.setTimer("resize_test", resize_test, 1000)
+
+# Main execution
+print("Creating advanced test scene...")
+mcrfpy.createScene("test")
+mcrfpy.setScene("test")
+
+# Schedule the test
+mcrfpy.setTimer("test_nested_clipping", test_nested_clipping, 100)
+
+print("Advanced test scheduled, running...")