Method copy

include/stringzilla/stringzilla.hpp:1647–1651

    std::size_t length() const noexcept { return first.size() + second.size(); }

    size_type copy(pointer destination) const noexcept {
        first.copy(destination);
        second.copy(destination + first.length());
        return first.length() + second.length();
    }

    size_type copy(pointer destination, size_type length) const noexcept {
        auto first_length = std::min(first.length(), length);