Method empty

include/boost/ut.hpp:524–524

  [[nodiscard]] constexpr std::size_t size() const noexcept { return N; }
  [[nodiscard]] constexpr bool empty() const noexcept { return N == 0; }
  [[nodiscard]] constexpr explicit operator std::string_view() const noexcept {
    return {_data, N};
  }