int != int32

During the `cupy` / `numpy` / `pk.array` usage, the developer should specify the `int` to `int32` instead of just `int`, because it may cause issues.

```python
# Incorrect
color_xp        = xp.zeros(N, dtype=xp.int)

# Correct
color_xp        = xp.zeros(N, dtype=xp.int32)
```