Use cuda 12.8

[ashwinvaidya17]

Summary

• Add index url for cuda 12.8 and xpu
• Now, the dependencies need to be specified as uv pip install -e .[cuda] or uv pip install -e .[xpu]

How to test

Checklist

• I have added unit tests to cover my changes.​
• I have added integration tests to cover my changes.​
• I have ran e2e tests and there is no issues.
• I have added the description of my changes into CHANGELOG in my target branch (e.g., CHANGELOG in develop).​
• I have updated the documentation in my target branch accordingly (e.g., documentation in develop).
• I have linked related issues.

License

• I submit my code changes under the same Apache License that covers the project.
  Feel free to contact the maintainers if that's a concern.
• I have updated the license header for each file (see an example below).

# Copyright (C) 2025 Intel Corporation
# SPDX-License-Identifier: Apache-2.0

[sovrasov]

Having introduced a new installation target, we need to update install instructions in the docs accordingly

[sovrasov]

Just tested torch+cu12_8 installation locally: it works for slightly outdated drivers (built for CUDA12.6). It looks like the PR doesn't brake at least CUDA12.x compatibility