Function dense_gemv_batch2 

pub fn dense_gemv_batch2(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    input: DevicePtr,
    weight: &DenseWeight,
    output: DevicePtr,
    n: u32,
    k: u32,
    out_stride: u32,
    stream: u64,
) -> Result<()>

2026-09-25: Dense BF16 GEMV for two rows in one pass over the weight. Each row follows dense_gemv_bf16’s K order and reduction (gb10 kernels).

input: [2, K] BF16, contiguous; output: two rows at output + t * out_stride (BF16 elements). The batched SSM decode uses it for a BF16 in_proj_qkvz (qwen3_ssm/trait_decode_batched.rs).

Kernel: dense_gemv_bf16_batch2(A, B, C, N, K, out_stride)