Method swap

libs/base/thread.hpp:104–104

  bool joinable() const noexcept { return m_thread.joinable(); }
  native_handle_type native_handle() { return m_thread.native_handle(); }
  void swap(SimpleThread & x) noexcept { m_thread.swap(x.m_thread); }

private:
  static void ThreadFunc(std::function<void()> && fn);