Fix stack overflow if many objects are fetched. (#237)

* fix stack overflow if many objects are fetched

* fix other stack allocations

* add tests and fix linting

* address stephanie's comments

* fix linting

* fix tests

src/numbuf/python/src/pynumbuf/numbuf.cc

@@ -320,8 +320,8 @@ static PyObject* retrieve_list(PyObject* self, PyObject* args) {
   if (!PyObjectToPlasmaConnection(plasma_conn, &conn)) { return NULL; }
 
   Py_ssize_t num_object_ids = PyList_Size(object_id_list);
-  object_id object_ids[num_object_ids];
-  object_buffer object_buffers[num_object_ids];
+  object_id* object_ids = new object_id[num_object_ids];
+  object_buffer* object_buffers = new object_buffer[num_object_ids];
 
   for (int i = 0; i < num_object_ids; ++i) {
     PyStringToUniqueID(PyList_GetItem(object_id_list, i), &object_ids[i]);
@@ -374,6 +374,9 @@ static PyObject* retrieve_list(PyObject* self, PyObject* args) {
     PyList_SetItem(returns, i, t);
   }
 
+  delete[] object_ids;
+  delete[] object_buffers;
+
   return returns;
 }