Make boltz install pytorch with cuda support on Windows with nvidia graphics

[Tom Goddard]

Currently the boltz install command will install boltz which has a dependency on torch and the default torch on Windows only has CPU support. If we detect Nvidia graphics we should install the cuda capable torch in the virtual environment before installing boltz so it can use the nvidia gpu. This requires a pip install (from ​https://pytorch.org/get-started/locally/) like

pip3 install torch --index-url ​https://download.pytorch.org/whl/cu126

This specifies cuda version 12.6. There are also 11.8 and 12.8 builds available. I'm not sure which are compatible. On our Linux system minsky we have CUDA 12.4 support from the nvidia driver but are using torch with cuda 12.6. I would think that the torch cuda should be no newer than the system cuda but apparently that is not required.

Probably I should also choose the cuda version when installing boltz on linux based on the system cuda version.