Make `requirements.txt` less strict to make `xcodec2` module usable

[3manifold]

requirements.txt for xcodec2==0.1.5 or xcodec2==0.1.3 is super strict regarding the large modules i.e. torch & cuda ones. This makes xcoded2 unusable since each time one tries to run it, he has to have the exact torch & cuda modules, elsewhere it will start downloading them which takes a serious amount of time.

For instance, are you sure that the xcodec2 module will not work if torch is not exactly on 2.5.0 version?

Please fix requirements.txt using >= etc.