feat(api): add plug_in_detection

src/types/usb_device.rs

@@ -93,7 +93,10 @@ impl<const L: usize> UsbDevice<L> {
         })
     }
 
-    #[inline]
+    #[inline(always)]
+    pub fn plug_in_detect(&self, cs: CriticalSection<'_>) -> bool {
+        self.usb.borrow(cs).usbsta.read().vbus().bit_is_set()
+    }
 
     #[inline(always)]
     pub(crate) fn allocated_endpoints(&self) -> impl Iterator<Item = (usize, &USBEndpoint)> {