Add cli kernel init

[MekkCyber]

This should init a kernel project with default templates to simplify a bit the copy/pasting.

Example:

/dev/kernels$ kernels init example-kernel

✅ Kernel project 'example-kernel' initialized successfully at: /dev/kernels/example-kernel

Project structure:
├── example_kernel_cuda
├── example_kernel_metal
├── example_kernel_rocm
├── example_kernel_xpu
├── torch-ext
│   ├── example_kernel
│   │   └── __init__.py
│   ├── torch_binding.cpp
│   └── torch_binding.h
├── .gitattributes
├── README.md
├── build.toml
└── flake.nix

Next steps:
  1. cd /dev/kernels/example-kernel
  2. Add your kernel implementation in example_kernel/
  3. Update torch-ext/example_kernel/__init__.py to export your functions
  4. Build with: nix run .#build-and-copy 
  5. Upload with: kernels upload . --repo-id your-username/example-kernel

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.