Use clean at::cuda::CUDAStream but not wrapped with std::optional

[youge325]

之前因为 at::cuda::CUDAStream 没有 operator= 重载导致无法直接赋值，因此使用了 std::optional 容器，实际上应该像原来一样使用初始化列表，通过 lambda 表达式返回一个用于构造函数重载的 Stream ，以此消除引入 std::optional 带来的 diff

[Copilot]

Pull request overview

This PR aims to remove the std::optional wrapper around at::cuda::CUDAStream by constructing comm_stream directly (via initializer-list + lambda), and updating stream usages accordingly.

Changes:

• Replace std::optional<at::cuda::CUDAStream> comm_stream with a plain at::cuda::CUDAStream.
• Initialize device_id and comm_stream in Buffer’s constructor initializer list.
• Update call sites from comm_stream.value() to comm_stream.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 15 comments.

File	Description
csrc/deep_ep.hpp	Changes Buffer to store comm_stream directly and adjusts accessors.
csrc/deep_ep.cpp	Moves stream/context setup into initializer list and updates many stream call sites.

Comments suppressed due to low confidence (2)

csrc/deep_ep.cpp:1447

• This internode::cached_notify call passes comm_stream (at::cuda::CUDAStream) where the API expects cudaStream_t (see csrc/kernels/api.cuh). Please pass comm_stream.stream() / get_comm_stream_raw() instead.

                             rank,
                             comm_stream,
                             config.get_rdma_buffer_size_hint(hidden_int4 * sizeof(int4), num_ranks),
                             num_nvl_bytes,
                             false,
                             low_latency_mode);

csrc/deep_ep.cpp:1127

• internode::cached_notify’s signature takes cudaStream_t stream (see csrc/kernels/api.cuh), but this call passes comm_stream (at::cuda::CUDAStream). This should be comm_stream.stream() / get_comm_stream_raw().

                                 barrier_signal_ptrs_gpu,
                                 rank,
                                 comm_stream,
                                 config.get_rdma_buffer_size_hint(hidden_int4 * sizeof(int4), num_ranks),
                                 num_nvl_bytes,
                                 true,
                                 low_latency_mode);

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