Function dense_gemm 

pub fn dense_gemm(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    input: DevicePtr,
    weight: &DenseWeight,
    output: DevicePtr,
    m: u32,
    n: u32,
    k: u32,
    stream: u64,
) -> Result<()>

2026-09-25: Scalar BF16 GEMM, C = A @ B^T (kernel dense_gemm_bf16(A, B, C, M, N, K)): A [M, K] row-major, B [N, K] row-major (HuggingFace layout), C [M, N] row-major.