[remux] don't listen for stylus events when hidden

this should save CPU (~6-7%) while the stylus is active and remux is not
showing.

src/remux/launcher.cpy

@@ -255,6 +255,7 @@ class App: public IApp:
     app_dialog->on_hide += PLS_LAMBDA(auto &d):
       self.render_bg()
       launch(CURRENT_APP)
+      ui::MainLoop::in.unmonitor(ui::MainLoop::in.wacom.fd)
       if USE_KOREADER_WORKAROUND and CURRENT_APP != "KOReader":
         ui::MainLoop::in.ungrab()
     ;
@@ -427,6 +428,7 @@ class App: public IApp:
     if ui::MainLoop::overlay_is_visible:
       return
 
+    ui::MainLoop::in.monitor(ui::MainLoop::in.wacom.fd)
     ClockWatch cz
 
     ClockWatch c0
@@ -796,6 +798,8 @@ class App: public IApp:
     ui::MainLoop::motion_event += PLS_DELEGATE(self.handle_motion_event)
     // ui::MainLoop::gesture_event += PLS_DELEGATE(self.handle_gesture_event)
 
+    ui::MainLoop::in.unmonitor(ui::MainLoop::in.wacom.fd)
+
     while true:
       ui::MainLoop::main()
       ui::MainLoop::check_resize()

src/rmkit/input/input.cpy

@@ -145,6 +145,9 @@ namespace input:
       FD_SET(fd,&rdfs)
       max_fd = max(max_fd, fd+1)
 
+    void unmonitor(int fd):
+      FD_CLR(fd, &rdfs)
+
     def handle_ipc():
       char buf[1024];
       int bytes = read(input::ipc_fd[0], buf, 1024);