Function group_unit 

pub fn group_unit<'a>(
    units: impl IntoIterator<Item = &'a ComputeUnit>,
) -> Option<ComputeUnit>

2026-10-02: The unit a plan group runs its node on, from its kernels’ units: tensor cores when any kernel issues MMAs (the others quantize, stage or reduce around it), else CUDA cores when any kernel computes, else memory. None for a group without kernels.