refactor: drop Boost.Move dependency

Implement constexpr definitions of forward and move to replace usage
of boost::move and boost::forward from the Boost.Move library.

Alter tests to use std::move instead of boost::move.

Remove the dependency on Boost.Move from build.jam

include/boost/optional/detail/optional_utility.hpp

@@ -0,0 +1,38 @@
+// Copyright (C) 2024 Andrzej Krzemienski.
+//
+// Use, modification, and distribution is subject to 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)
+//
+// See http://www.boost.org/libs/optional for documentation.
+//
+// You are welcome to contact the author at:
+//  akrzemi1@gmail.com
+
+#ifndef BOOST_OPTIONAL_OPTIONAL_DETAIL_OPTIONAL_UTILITY_HPP
+#define BOOST_OPTIONAL_OPTIONAL_DETAIL_OPTIONAL_UTILITY_HPP
+
+namespace boost {
+namespace optional_detail {
+
+// Workaround: forward and move aren't constexpr in C++11
+template <class T> inline constexpr T&& forward(typename boost::remove_reference<T>::type& t) noexcept
+{
+  return static_cast<T&&>(t);
+}
+
+template <class T> inline constexpr T&& forward(typename boost::remove_reference<T>::type&& t) noexcept
+{
+  BOOST_STATIC_ASSERT_MSG(!boost::is_lvalue_reference<T>::value, "Can not forward an rvalue as an lvalue.");
+  return static_cast<T&&>(t);
+}
+
+template <class T> inline constexpr typename boost::remove_reference<T>::type&& move(T&& t) noexcept
+{
+  return static_cast<typename boost::remove_reference<T>::type&&>(t);
+}
+
+} // namespace optional_detail
+} // namespace boost
+
+#endif