Feature/concurrent node containers (#271)

* added concurrent node containers

* removed spurious typename

* added missing includes

* avoided unused param warning

* worked around Clang bug

* s/{}/() to work around GCC4.8 problems with aggregate initialization

* used /bigobj for cfoa/visit_tests.cpp

* suppressed localized maybe-uninitialized warnings

* fixed comments

* added /bigobj to cfoa/insert_tests.cpp

* instrumented double exact comparison to spot a spurious error

* fixed pedantic error

* refactored byte_span machinery

* compromised on sub-epsilon equality for doubles that should be identical

* documented boost::concurrent_node_(map|set)

* added concurrent_node_set

* added missing AlternativeType

* tested empty node insertion

* tested node_handle allocator management

* added nonassignable_allocator and node_handle_allocator_swap_tests

* fixed warning disabling

* silenced spurious GCC warning

* broadened scope of previous pragma

* broadened even more

* worked around spurious constexpr-related msvc-14.0 bug
https://godbolt.org/z/v78545Ebf

* added workaround back

* replaced previous workaround with built-in one

* added workaround back on top of built-in solution (which doesn't work 100% of the time)

test/cfoa/serialization_tests.cpp

@@ -1,4 +1,4 @@
-// Copyright (C) 2023 Joaquin M Lopez Munoz
+// Copyright (C) 2023-2024 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)
 
@@ -12,6 +12,8 @@
 #include <boost/serialization/nvp.hpp>
 #include <boost/unordered/concurrent_flat_map.hpp>
 #include <boost/unordered/concurrent_flat_set.hpp>
+#include <boost/unordered/concurrent_node_map.hpp>
+#include <boost/unordered/concurrent_node_set.hpp>
 
 namespace {
 
@@ -70,11 +72,15 @@ namespace {
 
   boost::concurrent_flat_map<
     test::object, test::object, test::hash, test::equal_to>* test_flat_map;
+  boost::concurrent_node_map<
+    test::object, test::object, test::hash, test::equal_to>* test_node_map;
   boost::concurrent_flat_set<
     test::object, test::hash, test::equal_to>* test_flat_set;
+  boost::concurrent_node_set<
+    test::object, test::hash, test::equal_to>* test_node_set;
 
   UNORDERED_TEST(serialization_tests,
-    ((test_flat_map)(test_flat_set))
+    ((test_flat_map)(test_node_map)(test_flat_set)(test_node_set))
     ((text_archive)(xml_archive))
     ((default_generator)))
 }