Mostly remove pre-CXX11 workarounds.

С++03 support was deprecated in 1.85 and now can be removed. This PR clears
many of workarounds, which are no longer needed now.

* Remove unused workaround macros (many of).
* Remove BOOST_STATIC_ASSERT usages.
* Minimize Boost::type_traits dependency (in favour of STL's type_traits).

Closes https://github.com/boostorg/iterator/pull/82.

Squashed commit of the following:

commit 741a627b73
Author: Georgy Guminov <gogagum@gmail.com>
Date:   Sat Jan 25 12:13:05 2025 +0300

    Replace testers with standard metafunctions.

commit bf4cce6114
Author: Georgy Guminov <gogagum@gmail.com>
Date:   Sat Jan 25 11:51:32 2025 +0300

    Refactor is_lvalue_iterator.hpp.

commit 8d080c6c58
Author: Georgy Guminov <gogagum@gmail.com>
Date:   Sat Jan 25 10:27:32 2025 +0300

    Remove more workarounds.

commit 5a4ba24d36
Author: Georgy Guminov <gogagum@gmail.com>
Date:   Sun Jan 19 16:38:30 2025 +0300

    Fixes.

commit fdfafce2b9
Author: Georgy Guminov <gogagum@gmail.com>
Date:   Sat Oct 26 15:06:43 2024 +0300

    Remove BOOST_NO_STRICT_ITERATOR_INTEROPERABILITY
    Correct static_assert messages.
    Fix messages & replace is_standard_layout with is_copy_constructible.

commit c69ac1408a
Author: Georgy Guminov <gogagum@gmail.com>
Date:   Sat Oct 26 14:48:51 2024 +0300

    Correct static_assert messages.

commit b5df827151
Author: Georqy Guminov <gogagum@gmail.com>
Date:   Sun Jun 23 16:12:29 2024 +0300

    Fixes. Remove some Boost.MPL usages. Remove unused includes.

commit 01fd35e9f8
Author: Georgiy Guminov <gogagum@gmail.com>
Date:   Wed Jun 12 17:14:21 2024 +0300

    abstract conjunction.

commit c02def8acf
Author: Georgiy Guminov <gogagum@gmail.com>
Date:   Wed Jun 12 16:35:43 2024 +0300

    return addressof & conjunction.

commit 3b3d162575
Author: Georgiy Guminov <gogagum@gmail.com>
Date:   Wed Jun 12 16:30:44 2024 +0300

    Make macro more readable.

commit 4ab19e045f
Author: Georgiy Guminov <gogagum@gmail.com>
Date:   Wed Jun 12 15:56:49 2024 +0300

    Add static_assert messages.

commit 82b5c44cd3
Author: Georgiy Guminov <gogagum@gmail.com>
Date:   Wed Jun 12 14:12:10 2024 +0300

    Return is iterator CXX17 test.

commit 2d58d65462
Author: Georgiy Guminov <gogagum@gmail.com>
Date:   Tue Jun 11 14:04:17 2024 +0300

    Omitted.

commit a0d04d9491
Author: Georgiy Guminov <gogagum@gmail.com>
Date:   Tue Jun 11 14:00:35 2024 +0300

    Replace move with static_cast

commit 4a49b8a1a2
Author: Georgiy Guminov <gogagum@gmail.com>
Date:   Mon Jun 10 21:38:53 2024 +0300

    Return BOOST_NOEXCEPT

commit 054c013bba
Author: Georgiy Guminov <gogagum@gmail.com>
Date:   Sun Jun 9 15:20:41 2024 +0300

    CXX11

include/boost/iterator/counting_iterator.hpp

@@ -5,19 +5,14 @@
 #ifndef COUNTING_ITERATOR_DWA200348_HPP
 # define COUNTING_ITERATOR_DWA200348_HPP
 
+# include <type_traits>
+
 # include <boost/config.hpp>
-# include <boost/static_assert.hpp>
+# include <boost/detail/workaround.hpp>
 # ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
 # include <limits>
-# elif !BOOST_WORKAROUND(BOOST_BORLANDC, BOOST_TESTED_AT(0x551))
-# include <boost/type_traits/is_convertible.hpp>
-# else
-# include <boost/type_traits/is_arithmetic.hpp>
 # endif
-# include <boost/type_traits/is_integral.hpp>
 # include <boost/type_traits/type_identity.hpp>
-# include <boost/type_traits/conditional.hpp>
-# include <boost/type_traits/integral_constant.hpp>
 # include <boost/detail/numeric_traits.hpp>
 # include <boost/iterator/iterator_adaptor.hpp>
 
@@ -38,8 +33,6 @@ namespace detail
   template <class T>
   struct is_numeric_impl
   {
-      // For a while, this wasn't true, but we rely on it below. This is a regression assert.
-      BOOST_STATIC_ASSERT(::boost::is_integral<char>::value);
 
 # ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
 
@@ -50,11 +43,11 @@ namespace detail
 #  if !BOOST_WORKAROUND(BOOST_BORLANDC, BOOST_TESTED_AT(0x551))
       BOOST_STATIC_CONSTANT(
           bool, value = (
-              boost::is_convertible<int,T>::value
-           && boost::is_convertible<T,int>::value
+              std::is_convertible<int,T>::value
+           && std::is_convertible<T,int>::value
       ));
 #  else
-      BOOST_STATIC_CONSTANT(bool, value = ::boost::is_arithmetic<T>::value);
+      BOOST_STATIC_CONSTANT(bool, value = std::is_arithmetic<T>::value);
 #  endif
 
 # endif
@@ -62,7 +55,7 @@ namespace detail
 
   template <class T>
   struct is_numeric
-    : boost::integral_constant<bool, ::boost::iterators::detail::is_numeric_impl<T>::value>
+    : std::integral_constant<bool, ::boost::iterators::detail::is_numeric_impl<T>::value>
   {};
 
 #  if defined(BOOST_HAS_LONG_LONG)
@@ -116,7 +109,7 @@ namespace detail
   {
       typedef typename detail::ia_dflt_help<
           CategoryOrTraversal
-        , typename boost::conditional<
+        , typename std::conditional<
               is_numeric<Incrementable>::value
             , boost::type_identity<random_access_traversal_tag>
             , iterator_traversal<Incrementable>
@@ -125,7 +118,7 @@ namespace detail
 
       typedef typename detail::ia_dflt_help<
           Difference
-        , typename boost::conditional<
+        , typename std::conditional<
               is_numeric<Incrementable>::value
             , numeric_difference<Incrementable>
             , iterator_difference<Incrementable>
@@ -225,7 +218,7 @@ class counting_iterator
     difference_type
     distance_to(counting_iterator<OtherIncrementable, CategoryOrTraversal, Difference> const& y) const
     {
-        typedef typename boost::conditional<
+        typedef typename std::conditional<
             detail::is_numeric<Incrementable>::value
           , detail::number_distance<difference_type, Incrementable, OtherIncrementable>
           , detail::iterator_distance<difference_type, Incrementable, OtherIncrementable>