Class Deleter

Dependencies/napi/include/napi/napi.h:2073–2076

                       void* context,
                       void* data);
    struct Deleter {
      // napi_threadsafe_function is managed by Node.js, leave it alone.
      void operator()(napi_threadsafe_function*) const {};
    };

    std::unique_ptr<napi_threadsafe_function, Deleter> _tsfn;
    Deleter _d;