Fix Sprite texture setter 'error return without exception set'

Implemented the missing UISprite::set_texture method to properly:
- Validate the input is a Texture instance
- Update the sprite's texture using setTexture()
- Return appropriate error messages for invalid inputs

The setter now works correctly and no longer returns -1 without
setting an exception.

src/UISprite.cpp

@@ -162,7 +162,23 @@ PyObject* UISprite::get_texture(PyUISpriteObject* self, void* closure)
 
 int UISprite::set_texture(PyUISpriteObject* self, PyObject* value, void* closure)
 {
-    return -1;
+    // Check if value is a Texture instance
+    if (!PyObject_IsInstance(value, PyObject_GetAttrString(McRFPy_API::mcrf_module, "Texture"))) {
+        PyErr_SetString(PyExc_TypeError, "texture must be a mcrfpy.Texture instance");
+        return -1;
+    }
+    
+    // Get the texture from the Python object
+    auto pytexture = (PyTextureObject*)value;
+    if (!pytexture->data) {
+        PyErr_SetString(PyExc_ValueError, "Invalid texture object");
+        return -1;
+    }
+    
+    // Update the sprite's texture
+    self->data->setTexture(pytexture->data);
+    
+    return 0;
 }
 
 PyGetSetDef UISprite::getsetters[] = {