keyfork-qrcode: add framerate tracker for non-threaded

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

@@ -168,6 +168,7 @@ fn dbg_elapsed(count: u64, instant: Instant) {
     let elapsed = instant.elapsed().as_secs();
     let framerate = count as f64 / elapsed as f64;
     eprintln!("framerate: {count}/{elapsed} = {framerate}");
+    std::thread::sleep(std::time::Duration::from_secs(5));
 }
 
 /// Continuously scan the `index`-th camera for a QR code.
@@ -211,7 +212,7 @@ pub fn scan_camera(timeout: Duration, index: usize) -> Result<Option<String>, QR
         }
     }
 
-    // dbg_elapsed(count, start);
+    dbg_elapsed(count, start);
 
     Ok(None)
 }