Bug: `normalize_counts=False` zeroes out all sampling outputs

When `normalize_counts: false` in the data config, the sampling code silently zeroes out all generated samples and ground truth arrays.

**Root cause** in `sampling_generation.py`:
```python
if normalize_counts is not None:
    all_samples *= normalize_counts
    all_truths *= normalize_counts
```

Suggested fix:
```python
if normalize_counts is not None and normalize_counts is not False:

```