[client] app: delay showing the escape help for 250ms

This change prevents the help text being shown unless the escape key has
been held for a minimum of 250ms (reduced from 500ms).

client/src/main.h

@@ -51,6 +51,7 @@ struct AppState
   bool                 escapeActive;
   uint64_t             escapeTime;
   int                  escapeAction;
+  bool                 escapeHelp;
   KeybindHandle        bindings[KEY_MAX];
   const char *         keyDescription[KEY_MAX];
   bool                 keyDown[KEY_MAX];