Fixed std::initializer_list assignment issues for open-addressing containers (#277)

* fixed #276

* used range insert, stylistic this->

* assigned non-empty std::initializer_lists

test/objects/non_default_ctble_allocator.hpp

@@ -0,0 +1,46 @@
+
+// Copyright 2024 Joaquin M Lopez Munoz
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#if !defined(BOOST_UNORDERED_TEST_NON_DEFAULT_CTBLE_ALLOCATOR_HEADER)
+#define BOOST_UNORDERED_TEST_NON_DEFAULT_CTBLE_ALLOCATOR_HEADER
+
+#include <memory>
+
+namespace test
+{
+  template <class T> struct non_default_ctble_allocator
+  {
+    typedef T value_type;
+
+    non_default_ctble_allocator(int) {}
+
+    template <class U> 
+    non_default_ctble_allocator(const non_default_ctble_allocator<U>&) {}
+
+    template<class U>
+    bool operator==(non_default_ctble_allocator<U> const &) const noexcept
+    {
+      return true;
+    }
+
+    template<class U>
+    bool operator!=(non_default_ctble_allocator<U> const &) const noexcept
+    {
+      return false;
+    }
+    
+    T* allocate(std::size_t n)
+    {
+      return std::allocator<T>().allocate(n); 
+    }
+
+    void deallocate(T* p, std::size_t n)
+    {
+      std::allocator<T>().deallocate(p, n); 
+    }
+  };
+}
+
+#endif