feat: add nccl-extensions dependency

[kingchc]

What does this PR do ?

Adds nccl-extensions==0.1.0 as a Linux dependency for x86_64 and aarch64 systems, and updates uv.lock with the published wheels.

This makes the native nccl.m2n.reshard implementation available to the nccl_reshard refit transport without a separate package installation.

Issues

N/A

Usage

No usage change is required. Configure the existing transport as usual:

policy:
  generation:
    refit_transport: nccl_reshard

Before your PR is "Ready for review"

Pre checks:

• Read and followed the contributor guidelines.
• No new tests are required for this dependency-only change.
• Ran uv lock --check with Python 3.13.14.
• No documentation update is required because the existing nccl_reshard interface is unchanged.

Additional Information

Validated manually with four GB200 GPUs using Python 3.13.14, Torch 2.11.0+cu130, CUDA 13.0, NCCL 2.30.7, nccl4py==0.3.1, and nccl-extensions==0.1.0.

The four-rank cross-dimension nccl.m2n.reshard benchmark completed successfully with validation enabled.

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