use const refs in for loops for non tiny types

src/debug_utilities/object_sizes.cpp

@@ -51,7 +51,7 @@ class size_logger
 public:
   ~size_logger()
   {
-    for (const auto i: types)
+    for (const auto &i: types)
       std::cout << std::to_string(i.first) << "\t" << i.second << std::endl;
   }
   void add(const char *type, size_t size) { types.insert(std::make_pair(size, type)); }