Function process

test/anyflow/test_processor.cpp:403–406

       downstream_function_run_aftert_return_to_avoid_stack_overflow) {
  struct F1 : public GraphProcessor {
    virtual int process() noexcept override {
      *x.emit() = *a;
      return 0;
    }
    ANYFLOW_INTERFACE(ANYFLOW_DEPEND_DATA(int32_t, a)
                          ANYFLOW_EMIT_DATA(int32_t, x))
  };