Stash fd in epoll_event instead of pointer in server

src/server.hpp

@@ -118,10 +118,6 @@ private:
   std::vector<int> epoll_fds_;
   int listen_sockfd_ = -1;
 
-  // Unique tags for special events to avoid type confusion in epoll data union
-  static inline const char listen_socket_tag = 0;
-  static inline const char shutdown_pipe_tag = 0;
-
   // Private helper methods
   void setup_shutdown_pipe();
   void setup_signal_handling();