Implement Entity.index() method for Issue #73

Added index() method to Entity class that returns the entity's
position in its parent grid's entity collection. This enables
proper entity removal patterns using entity.index().

src/UIEntity.cpp

@@ -36,6 +36,33 @@ PyObject* UIEntity::at(PyUIEntityObject* self, PyObject* o) {
 
 }
 
+PyObject* UIEntity::index(PyUIEntityObject* self, PyObject* Py_UNUSED(ignored)) {
+    // Check if entity has an associated grid
+    if (!self->data || !self->data->grid) {
+        PyErr_SetString(PyExc_RuntimeError, "Entity is not associated with a grid");
+        return NULL;
+    }
+    
+    // Get the grid's entity collection
+    auto entities = self->data->grid->entities;
+    if (!entities) {
+        PyErr_SetString(PyExc_RuntimeError, "Grid has no entity collection");
+        return NULL;
+    }
+    
+    // Find this entity in the collection
+    int index = 0;
+    for (auto it = entities->begin(); it != entities->end(); ++it, ++index) {
+        if (it->get() == self->data.get()) {
+            return PyLong_FromLong(index);
+        }
+    }
+    
+    // Entity not found in its grid's collection
+    PyErr_SetString(PyExc_ValueError, "Entity not found in its grid's entity collection");
+    return NULL;
+}
+
 int UIEntity::init(PyUIEntityObject* self, PyObject* args, PyObject* kwds) {
     //static const char* keywords[] = { "x", "y", "texture", "sprite_index", "grid", nullptr };
     //float x = 0.0f, y = 0.0f, scale = 1.0f;
@@ -211,6 +238,7 @@ int UIEntity::set_spritenumber(PyUIEntityObject* self, PyObject* value, void* cl
 
 PyMethodDef UIEntity::methods[] = {
     {"at", (PyCFunction)UIEntity::at, METH_O},
+    {"index", (PyCFunction)UIEntity::index, METH_NOARGS, "Return the index of this entity in its grid's entity collection"},
     {NULL, NULL, 0, NULL}
 };
 

src/UIEntity.h

@@ -47,6 +47,7 @@ public:
     UIEntity(UIGrid&);
     
     static PyObject* at(PyUIEntityObject* self, PyObject* o);
+    static PyObject* index(PyUIEntityObject* self, PyObject* Py_UNUSED(ignored));
     static int init(PyUIEntityObject* self, PyObject* args, PyObject* kwds);
 
     static PyObject* get_position(PyUIEntityObject* self, void* closure);