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/detail/json_pointer.hpp

@@ -322,6 +322,8 @@ class json_pointer
         typename BasicJsonType::size_type idx{};
         switch (parse_array_index<BasicJsonType>(s, idx))
         {
+            // the branches differ in their messages, not after JSON_THROW's expansion
+            // NOLINTNEXTLINE(bugprone-branch-clone)
             case array_index_status::leading_zero:
                 JSON_THROW(detail::parse_error::create(106, 0, detail::concat("array index '", s, "' must not begin with '0'"), nullptr));
             case array_index_status::not_a_number:
@@ -685,6 +687,8 @@ class json_pointer
                     typename BasicJsonType::size_type idx{};
                     switch (parse_array_index<BasicJsonType>(reference_token, idx))
                     {
+                        // the branches differ in their messages, not after JSON_THROW's expansion
+                        // NOLINTNEXTLINE(bugprone-branch-clone)
                         case array_index_status::leading_zero:
                             JSON_THROW(detail::parse_error::create(106, 0, detail::concat("array index '", reference_token, "' must not begin with '0'"), nullptr));
                         case array_index_status::not_a_number: