Add TODOs for missing Py_DECREF specializations

These aren't necessary for correctness, just performance.

Include/internal/pycore_object.h

@@ -210,6 +210,7 @@ _Py_DECREF_NO_DEALLOC(PyObject *op)
 }
 
 #else
+// TODO: implement Py_DECREF specializations for Py_NOGIL build
 static inline void
 _Py_DECREF_SPECIALIZED(PyObject *op, const destructor destruct)
 {

Python/ceval.c

@@ -52,6 +52,7 @@
 // the limit of PGO, and that limit cannot be configured.
 // Define them as macros to make sure that they are always inlined by the
 // preprocessor.
+// TODO: implement Py_DECREF macro for Py_NOGIL
 
 #undef Py_DECREF
 #define Py_DECREF(arg) \