Function moe_fp8_grouped_sort 

pub fn moe_fp8_grouped_sort(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    out: Fp8GroupedSortOut,
    topk_ids: DevicePtr,
    total_expanded: u32,
    num_experts: u32,
    top_k: u32,
    stream: u64,
) -> Result<()>

2026-09-27: Sorts the total_expanded slots of topk_ids by expert, as moe_sort_by_expert does, and writes active_experts[0..count] in ascending order with active_count[0] = count, in one launch on stream (the grouped kernels that read them must follow on it).