Small error in lab_two

Error when using np.histogram2d with PyTorch tensors
<img width="1789" height="332" alt="Image" src="https://github.com/user-attachments/assets/52dfb2e7-9600-4c27-9118-7a53fe021282" />
We should replace 
```samples = sampleable.sample(num_samples).detach().cpu() # (ns, 2)```
with
```samples = sampleable.sample(num_samples).detach().cpu().numpy()```