Auto detect cuda in install script

[larryliu0820]

This pull request simplifies the process for building ExecuTorch with CUDA support by removing the requirement to set the CMAKE_ARGS environment variable. Now, CUDA support is automatically detected and handled during installation, streamlining both CI workflows and installation logic. Additionally, related documentation and error messages have been updated for clarity.

CI/CD and Installation Process Simplification

• Removed the need to set CMAKE_ARGS="-DEXECUTORCH_BUILD_CUDA=ON" in CI scripts and workflow files; install_executorch.sh now handles CUDA detection automatically. (.ci/scripts/test-cuda-build.sh, .github/workflows/cuda.yml) [1] [2] [3] [4] [5]
• Deleted the _is_cuda_enabled() function from install_utils.py and refactored logic to rely solely on CUDA detection via nvcc. [1] [2] [3]

Error Handling and Messaging Improvements

• Updated error messages in install_utils.py to remove references to "CUDA delegate" and clarify instructions for users when CUDA is not detected or supported.

Internal Refactoring

• Applied functools.lru_cache to _get_cuda_version() for more efficient repeated CUDA version detection.

These changes make the CUDA build process more user-friendly and reduce the risk of misconfiguration.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/15027

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