Add nvidia.com-cuda devcontainer feature

[Copilot]

Adds a new community devcontainer feature that installs the NVIDIA CUDA Toolkit via NVIDIA's official apt repository.

Feature: nvidia.com-cuda

• src/nvidia.com-cuda/devcontainer-feature.json — Feature manifest with a version option accepting "latest" or "X.Y" format (e.g. "12.6"); proposals cover CUDA 11.8–12.6
• src/nvidia.com-cuda/install.sh — Detects distro (Ubuntu 20.04/22.04/24.04, Debian 11/12) and arch (x86_64, aarch64→sbsa), installs the NVIDIA CUDA apt keyring, then installs cuda-toolkit or cuda-toolkit-X-Y for a pinned version
• test/nvidia.com-cuda/test.sh — Verifies nvcc --version succeeds post-install
• .github/workflows/test.yaml — Adds nvidia.com-cuda to both test-autogenerated and test-scenarios matrix jobs

Usage

// devcontainer.json
{
  "features": {
    "ghcr.io/devcontainer-community/features/nvidia.com-cuda:1": {
      "version": "12.6"   // or "latest"
    }
  }
}

The keyring URL is parameterised via cuda_keyring_version so bumping the keyring package requires a one-line change.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add feature nvidia.com-cuda</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add feature nvidia.com-cuda #29

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[sebst]

@copilot Tests for nvidia.com-cuda are failing:

🔄 Testing 'nvcc installed'

bash: line 1: nvcc: command not found`

[Copilot]

@copilot Tests for nvidia.com-cuda are failing:

...

Fixed in commit 5805b01. The CUDA toolkit installs nvcc to /usr/local/cuda/bin/ which isn't in the default PATH. Two changes in install.sh:

1. Creates /etc/profile.d/cuda.sh prepending /usr/local/cuda/bin to PATH for interactive shells
2. Symlinks /usr/local/bin/nvcc → /usr/local/cuda/bin/nvcc so nvcc is immediately available in non-interactive shells (including the test runner)