• added: Derive Clone and Copy for AppendHeaders (#2776)
• added: must_use attribute on AppendHeaders (#2846)
• added: must_use attribute on ErrorResponse (#2846)
• added: must_use attribute on IntoResponse::into_response (#2846)
• added: must_use attribute on IntoResponseParts trait methods (#2846)
• added: Implement Copy for DefaultBodyLimit (#2875)
• added: DefaultBodyLimit::max and DefaultBodyLimit::disable are now
  allowed in const context (#2875)