Update `numpy.warnings` to use built-in `warnings` module

[quattro]

Numpy dropped the numpy.warnings sub-module in version 1.24. It looks like it was just an alias for the built-in module warnings, so we can swap it out as-is. This affects the code here:

ma-focus/pyfocus/data/exprref.py

Line 95 in 2cea17d

with np.warnings.catch_warnings():