Fix support for CUDA 12.6 and finding CUDA tools

[mgorny]

Checklist

• Used a personal fork of the feedstock to propose changes
• Bumped the build number (if the version is unchanged)
• Reset the build number to 0 (if the version changed)
• Re-rendered with the latest conda-smithy (Use the phrase @conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• Ensured the license file is being packaged.

Unfortunately, my testing of #26 was insufficient, and more complex testing with PyTorch revealed more issues. This pull request:

1. Backports an upstream patch enabling support for CUDA 12.6.
2. Fixes tool path lookup to use PATH, to find tools installed in CONDA_PREFIX.
3. Adds a minimal pytest invocation that would have caught the two aforementioned bugs.

[conda-forge-admin]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe/meta.yaml) and found it was in an excellent condition.

[h-vetinari]

Nice, thanks!

[mgorny]

Thank you!