Add option for CUDA 13.1 llama.cpp in installer

[GodEmperor785]

This PR adds new choice for NVIDIA option in installer - choose CUDA version for llama.cpp. Other options are unchanged.

So now choices looks like this when user selects "A) NVIDIA" when installing they have another choice:

Which CUDA version do you want for llama.cpp?

A) CUDA 12.4 - Supports all GPUs
B) CUDA 13.1 - Faster on RTX 50xx Blackwell, but drops GTX 750/900/1000 and Titan V (needs driver >= 580)

https://github.com/oobabooga/llama-cpp-binaries already provides builds for CUDA 13.1 for llama.cpp, also portable builds provide version with CUDA 13.1.

Made this as a choice for user because some people might have old GPUs or just might want to install old builds for some reason.

For users with existing installation it doesn't reinstall anything - old installs will stay on 12.4. User can always delete installer_files and reinstall for CUDA 13.1

I verified locally that installation of CUDA 12.4/13.1 binaries works (fresh install) and that running from old install still works. Tested on Windows + Nvidia GPU.

Checklist:

• I have read the Contributing guidelines.