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/reentrancy_check_test.cpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Joaquin M Lopez Munoz
+// Copyright 2023-2024 Joaquin M Lopez Munoz
 // Distributed under the Boost Software License, Version 1.0.
 // https://www.boost.org/LICENSE_1_0.txt
 
@@ -32,15 +32,21 @@ namespace boost {
 
 #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>
 #include <boost/core/lightweight_test.hpp>
 
 using test::default_generator;
 
 using map_type = boost::unordered::concurrent_flat_map<raii, raii>;
+using node_map_type = boost::unordered::concurrent_node_map<raii, raii>;
 using set_type = boost::unordered::concurrent_flat_set<raii>;
+using node_set_type = boost::unordered::concurrent_node_set<raii>;
 
 map_type* test_map;
+map_type* test_node_map;
 set_type* test_set;
+node_set_type* test_node_set;
 
 template<typename F>
 void detect_reentrancy(F f)
@@ -105,7 +111,7 @@ namespace {
 // clang-format off
 UNORDERED_TEST(
   reentrancy_tests,
-  ((test_map)(test_set))
+  ((test_map)(test_node_map)(test_set)(test_node_set))
   ((value_type_generator_factory))
   ((default_generator)))
 // clang-format on