fix pytorch UserWarning

[hushaoqing]

fix #8

test

Windows 11 WSL, Python 3.10.15 x64, Numpy 1.26.4, 12th Gen Intel(R) Core(TM) i7-12700KF 3.60 GHz:

numpy.save: 0:00:00.657019
fastnumpyio.save: 0:00:00.185535
fastnumpyio.pack: 0:00:00.157975
numpy.load: 0:00:01.783694
fastnumpyio.load: 0:00:00.257334
fastnumpyio.unpack: 0:00:00.175327
numpy.save+numpy.load == fastnumpyio.save+fastnumpyio.load: True
numpy.save+numpy.load == fastnumpyio.pack+fastnumpyio.unpack: True