Fix Entity property setters and PyVector implementation

Fixed the 'new style getargs format' error in Entity property setters by:
- Implementing PyObject_to_sfVector2f/2i using PyVector::from_arg
- Adding proper error checking in Entity::set_position
- Implementing PyVector get_member/set_member for x/y properties
- Fixing PyVector::from_arg to handle non-tuple arguments correctly

Now Entity.pos and Entity.sprite_number setters work correctly with
proper type validation.

tests/entity_setter_simple_test.py

@@ -0,0 +1,61 @@
+#!/usr/bin/env python3
+"""
+Simple test for Entity property setters
+"""
+
+def test_entity_setters(timer_name):
+    """Test Entity property setters"""
+    import mcrfpy
+    import sys
+    
+    print("Testing Entity property setters...")
+    
+    # Create test scene and grid
+    mcrfpy.createScene("test")
+    ui = mcrfpy.sceneUI("test")
+    
+    # Create grid with texture
+    texture = mcrfpy.Texture("assets/kenney_ice.png", 16, 16)
+    grid = mcrfpy.Grid(10, 10, texture, (10, 10), (400, 400))
+    ui.append(grid)
+    
+    # Create entity
+    entity = mcrfpy.Entity((2.5, 3.5), texture, 5, grid)
+    grid.entities.append(entity)
+    
+    # Test 1: Initial position
+    print(f"Initial position: {entity.pos}")
+    print(f"Initial position x={entity.pos.x}, y={entity.pos.y}")
+    
+    # Test 2: Set position with Vector
+    entity.pos = mcrfpy.Vector(4.0, 5.0)
+    print(f"After Vector setter: pos={entity.pos}, x={entity.pos.x}, y={entity.pos.y}")
+    
+    # Test 3: Set position with tuple
+    entity.pos = (7.5, 8.5)
+    print(f"After tuple setter: pos={entity.pos}, x={entity.pos.x}, y={entity.pos.y}")
+    
+    # Test 4: sprite_number
+    print(f"Initial sprite_number: {entity.sprite_number}")
+    entity.sprite_number = 10
+    print(f"After setter: sprite_number={entity.sprite_number}")
+    
+    # Test 5: Invalid types
+    try:
+        entity.pos = "invalid"
+        print("ERROR: Should have raised TypeError")
+    except TypeError as e:
+        print(f"✓ Correctly rejected invalid position: {e}")
+    
+    try:
+        entity.sprite_number = "invalid"
+        print("ERROR: Should have raised TypeError")
+    except TypeError as e:
+        print(f"✓ Correctly rejected invalid sprite_number: {e}")
+    
+    print("\n✅ Entity property setters test completed")
+    sys.exit(0)
+
+# Execute the test after a short delay
+import mcrfpy
+mcrfpy.setTimer("test", test_entity_setters, 100)