fw-rust: Improve debouncing when going back

When pressing the button until the timer1 creates an interrupt in
order to create a "back" event, there were some debouncing problems.

firmware/rust/src/main.rs

@@ -160,6 +160,7 @@ impl ClockGenerator {
                 if self.tc1.tccr1b.read().cs1().is_prescale_64() {
                     self.tc1.tccr1b.write(|w| w.cs1().no_clock());
                     self.screen.input(&Input::Select);
+                    self.delay.delay_ms(3_u8);
                 }
             }
             UPDATE_BUTTON.store(false, Ordering::SeqCst);