Function q2_0_mmq_gemm_packed 

pub fn q2_0_mmq_gemm_packed(
    gpu: &dyn GpuBackend,
    kernel_nc: KernelHandle,
    kernel_wc: KernelHandle,
    a_q8: DevicePtr,
    w: &PackedQ2Weight,
    out_bf16: DevicePtr,
    m: u32,
    stream: u64,
) -> Result<()>

2026-09-25: q2_0_mmq_gemm on a PackedQ2Weight. Returns an error unless w.group == 128, the group size of block_q2_0.