请求了 CPU `gemm_4bit_forward` 内核,但没有指定 `backend="cpu"`,因此在 CUDA torch 构建中永远不会加载

`bitsandbytes/backends/cpu/ops.py` requests the fused CPU 4-bit gemm kernel without specifying a backend. `kernels` therefore infers the backend from the installed torch build, which on any CUDA wheel is a CUDA backend — and `kernels-community/quantization-bitsandbytes` publishes CPU-only build variants. Every variant is rejected, `get_kernel` raises, and the `except Exception` handler logs a warning on every process start on any host whose CPU reports AVX512-BF16.