define copy constructor for NAlloc

tests/src/unit-allocator.cpp

@@ -283,11 +283,16 @@ struct NAlloc
     };
 
     NAlloc() :
-        alloc(), m_alloc_size(0)
+        alloc()
     {
 
     }
 
+    NAlloc(const NAlloc&) = default;                   // Copy constructor
+    NAlloc(NAlloc&&) = default;                       // Move constructor
+    NAlloc& operator=(const NAlloc& other) = default;  // Copy assignment operator
+    NAlloc& operator=(NAlloc&&) = default;            // Move assignment operator
+
     virtual ~NAlloc() = default;
 
     pointer allocate(std::size_t n)