perf: block event loop with -1 timeout instead of spinning

Use epoll blocking dispatch so the compositor sleeps when idle.
WINGs timers and frame callbacks still wake the loop as needed.

src/backend/wayland/wl_backend.c

@@ -1141,7 +1141,7 @@ wl_event_loop_run(void)
             wl_display_flush_clients(wl_state.display);
             extern void W_WLClientDispatchPending(void);
             W_WLClientDispatchPending();
-            wl_event_loop_dispatch(loop, 4);
+            wl_event_loop_dispatch(loop, -1);  /* block until fd ready */
 
             /* Check inotify for defaults database changes */
 #ifdef HAVE_INOTIFY