BUG: Change in handling of -1 in np.uint arrays between NumPy version 1.x and 2.x

[q-pratz-chem]

Describe the problem:

An OverflowError was encountered while running the base.py script, where an attempt was made to generate the indices_multi NumPy array with type np.uint8 that included negative values. This behavior was observed to differ from that of NumPy version 1.22.4, Python 3.9.12, where the same operation was executed without issue.

Code that reproduces the bug:

import numpy as np
dict_ = {5: np.array([0, 4, -1, 6, 8, -8], dtype=np.uint8)}

Traceback error:

OverflowError: Python integer -1 out of bounds for uint8

Package versions:

python: 3.9.20
fanpy: 1.0.0
numpy: 2.0.2

Additonal comments

This issue appears to be related to the change in promotion rules for Python scalars in NumPy arrays between version 1.x and 2.x.

[q-pratz-chem]

NEP 50 — Promotion rules for Python scalars talks about the details of the change in promotion rules for Python Scalars.

In the case of the fanpy/wfn/cc/base.py, replacing np.uint with np.int seems to handle the issue.