Fix the library warnings and noexcept specifications from the merged PRs

- binary_reader: rename the error_handler constructor parameter, which
  shadowed the member (-Wshadow, -Wshadow-field-in-constructor; #5746)
- basic_json(copy_construct_tag, ...): declare it noexcept when copying
  the base class is (GCC 16 -Wnoexcept; #5690)
- the scalar-on-left legacy comparison operators: noexcept only when
  converting the scalar is, like their member counterparts (#5682, #5751)
- compare_leaves: use std::is_eq/is_lt/is_gt instead of comparing a
  std::partial_ordering with 0 (-Wzero-as-null-pointer-constant; #5686)
- serializer: silence MSVC C4127 for the EnsureAscii template parameter
  (#5741, #5746)
- clang-tidy: return the sanitized reference in binary_writer, take the
  key of ordered_map::find_impl by const reference (#5727), and mark the
  switches over parse_array_index (#5728)
- ordered_map: keep <memory> for std::allocator (IWYU)

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

include/nlohmann/ordered_map.hpp

@@ -12,7 +12,7 @@
 #include <functional> // equal_to, less
 #include <initializer_list> // initializer_list
 #include <iterator> // input_iterator_tag, iterator_traits
-#include <memory> // allocator
+#include <memory> // allocator // IWYU pragma: keep
 #include <new> // for operator new (placement new)
 #include <stdexcept> // for out_of_range
 #include <tuple> // forward_as_tuple
@@ -78,7 +78,7 @@ private:
     /// @brief find the entry for @a key, for either constness of @a self
     /// @note the single place that performs the linear key search
     template<typename Self, typename KeyType>
-    static auto find_impl(Self& self, KeyType&& key) -> decltype(self.begin())
+    static auto find_impl(Self& self, const KeyType& key) -> decltype(self.begin())
     {
         for (auto it = self.begin(); it != self.end(); ++it)
         {