Skip cuda-specific dependencies on a non-Linux OS

[raulchen]

Some SkyRL dependencies are only available on CUDA.
This PR adds conditions for these dependencies.
So uv sync --active --extra vllm would work on macOS.
Note, we still cannot run SkyRL on macOS, unless we make the imports optional.
But it would make local development easier by allowing navigating the codebase.

[gemini-code-assist]

Code Review

This pull request aims to make CUDA-specific dependencies optional on non-Linux systems. While it correctly adds platform markers for several packages, it misses some key Linux-only dependencies like vllm, sglang, and transformer-engine. Without these changes, the goal of enabling dependency installation on macOS will not be fully achieved. I've added critical comments to address these omissions. I also have a suggestion to improve the maintainability of the configuration.

[gemini-code-assist]

The vllm package is only available for Linux. To achieve the goal of this PR and allow installation on other platforms like macOS, you should add a platform marker to this dependency as well.

    "vllm==0.11.0; sys_platform == 'linux'",

[gemini-code-assist]

The sglang package is only available for Linux. To allow installation on other platforms, you should add a platform marker to this dependency.

    "sglang[srt,openai,torch_memory_saver]==0.4.8.post1; sys_platform == 'linux'",

[gemini-code-assist]

The transformer-engine and vllm packages are Linux-only. To ensure the dependencies can be resolved on non-Linux systems, you should add platform markers to them.

  "transformer-engine[pytorch]==2.7.0; sys_platform == 'linux'",
  "flash-attn==2.7.4.post1; sys_platform == 'linux'",
  "vllm==0.10.1.1; sys_platform == 'linux'",

[gemini-code-assist]

For better readability and maintainability, you can combine these two flashinfer-python source definitions into a single entry. Since they point to the same URL and the mcore and sglang extras are mutually exclusive according to your [tool.uv].conflicts configuration, their markers can be simplified and merged.

    { url = "https://download.pytorch.org/whl/cu128/flashinfer/flashinfer_python-0.2.6.post1%2Bcu128torch2.7-cp39-abi3-linux_x86_64.whl", marker = "(extra == 'mcore' or extra == 'sglang') and sys_platform == 'linux'" }