Error in examples/demo.ipynb testing on a batch

In "Testing on a batch":

```python
fig = plt.figure(figsize=(10, 5))
for i, pred in enumerate(preds):
plt.subplot(1, 2, i + 1)
plt.imshow(frames[1])
plt.title(f'frame[{i}]')
for detection in pred:
plt.scatter(detection[:,0], detection[:,1], 2)
```
the 2nd loop is redundant, need to plot `pred[:, 0], pred[:, 1]` only.

Open examples/demo.ipynb, locate the 'Testing on a batch' section. The issue points to a redundant loop: instead of iterating over detections, plot pred[:,0] and pred[:,1] directly. Check the surrounding code to understand the data shape, then correct the plotting. Run the notebook cell to verify the fix produces the expected visualization.

索引モデルが issue の本文から書いたものです。