Implement EntityCollection.extend() method for Issue #27

Added extend() method to EntityCollection that accepts any iterable
of Entity objects and adds them all to the collection. The method:
- Accepts lists, tuples, generators, or any iterable
- Validates all items are Entity objects
- Sets the grid association for each added entity
- Properly handles errors and empty iterables

closes #27

src/UIGrid.cpp

@@ -637,9 +637,47 @@ PyObject* UIEntityCollection::remove(PyUIEntityCollectionObject* self, PyObject*
     return Py_None;
 }
 
+PyObject* UIEntityCollection::extend(PyUIEntityCollectionObject* self, PyObject* o)
+{
+    // Accept any iterable of Entity objects
+    PyObject* iterator = PyObject_GetIter(o);
+    if (iterator == NULL) {
+        PyErr_SetString(PyExc_TypeError, "UIEntityCollection.extend requires an iterable");
+        return NULL;
+    }
+    
+    PyObject* item;
+    while ((item = PyIter_Next(iterator)) != NULL) {
+        // Check if item is an Entity
+        if (!PyObject_IsInstance(item, PyObject_GetAttrString(McRFPy_API::mcrf_module, "Entity"))) {
+            Py_DECREF(item);
+            Py_DECREF(iterator);
+            PyErr_SetString(PyExc_TypeError, "All items in iterable must be Entity objects");
+            return NULL;
+        }
+        
+        // Add the entity to the collection
+        PyUIEntityObject* entity = (PyUIEntityObject*)item;
+        self->data->push_back(entity->data);
+        entity->data->grid = self->grid;
+        
+        Py_DECREF(item);
+    }
+    
+    Py_DECREF(iterator);
+    
+    // Check if iteration ended due to an error
+    if (PyErr_Occurred()) {
+        return NULL;
+    }
+    
+    Py_INCREF(Py_None);
+    return Py_None;
+}
+
 PyMethodDef UIEntityCollection::methods[] = {
     {"append", (PyCFunction)UIEntityCollection::append, METH_O},
-    //{"extend", (PyCFunction)UIEntityCollection::extend, METH_O}, // TODO
+    {"extend", (PyCFunction)UIEntityCollection::extend, METH_O},
     {"remove", (PyCFunction)UIEntityCollection::remove, METH_O},
     {NULL, NULL, 0, NULL}
 };

src/UIGrid.h

@@ -77,6 +77,7 @@ class UIEntityCollection {
 public:
     static PySequenceMethods sqmethods;
     static PyObject* append(PyUIEntityCollectionObject* self, PyObject* o);
+    static PyObject* extend(PyUIEntityCollectionObject* self, PyObject* o);
     static PyObject* remove(PyUIEntityCollectionObject* self, PyObject* o);
     static PyMethodDef methods[];
     static PyObject* repr(PyUIEntityCollectionObject* self);