keyfork-qrcode: add threaded handler

crates/qrcode/keyfork-qrcode/src/lib.rs

@@ -285,6 +285,9 @@ pub fn scan_camera(timeout: Duration, index: usize) -> Result<Option<String>, QR
 
         // dbg_elapsed(count, start);
 
+        arced.0.lock().expect(bug::bug!(POISONED_MUTEX)).shutdown = true;
+        arced.1.notify_all();
+
         Ok(None)
     })
 }