[ckpt] feat: add kimi ckpt engine backend

[kip-cxj]

What does this PR do?

Based on ckpt engine abstraction add checkpoint-engine abstraction, in this PR, we add kimi_ckpt_engine backend to support both GPU and huawei Ascend NPU.

Since establishing communication domains across trainer and rollout workers is required, this PR also depends on the newly added communication domain support in kimi_ckpt_engine.

TODO:

• Add detailed performance testing results in checkpoint engine README.

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Test

We have verified the functionality on both GPU and NPU. Performance benchmarks on a 32 NPU environment show promising results; however, due to a lack of available GPU resources, performance data for GPU is still pending.

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[gemini-code-assist]

Code Review

This pull request introduces a new checkpoint engine backend, kimi_ckpt_engine, designed to support both GPU and Huawei Ascend NPU environments. The implementation is comprehensive, including the core engine logic, integration with the existing checkpointing framework, and a new test suite. My review focuses on ensuring correctness and maintainability. I've identified a critical thread-safety issue in the weight sending logic that could lead to data corruption. Additionally, I've suggested a minor but important rename in the test suite to improve clarity.

[wuxibin89]

Why we need to offload model to CPU first? Does kimi ckpt engine support D2D?

[kip-cxj]

The kimi_checkpoint_engine only supports reading weights from the CPU. It first register all weights and all gather the metadata across all ranks.

[wuxibin89]

Please format code first.

[wuxibin89]

Could you provide more details about how kimi_ckpt_engine works? For example, give an image to show the communication topology between trainer and rollout workers.

[kip-cxj]

I have updated the description and added a schematic. Could you please review it again to see if the level of detail is sufficient? Also, I’ve been scheduled for the H100 environment and will supplement the performance data over the next two days.