Function w4a4_gemm_mfast 

pub fn w4a4_gemm_mfast(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    a_packed: DevicePtr,
    a_scale: DevicePtr,
    weight: &QuantizedWeight,
    output: DevicePtr,
    m: u32,
    n: u32,
    k: u32,
    stream: u64,
) -> Result<()>

2026-09-25: w4a4_gemm through the w4a4_gemm_mfast kernel, with M on the fast grid axis (blockIdx.x = M block), so consecutive CTAs share a B panel.