Method __run

include/stdexec/__detail/__spawn.hpp:91–101

      {}

      void __run() noexcept
      {
        if (__assoc_)
        {
          start(__op_);
        }
        else
        {
          __complete();
        }
      }

     private:
      using __assoc_t = std::remove_cvref_t<decltype(__declval<_Token&>().try_associate())>;