Function build_contract_key 

pub fn build_contract_key(
    dtype_tag: &'static str,
    modes_a: &[i32],
    modes_b: &[i32],
    modes_c: &[i32],
    extent_a: &[i64],
    extent_b: &[i64],
    extent_c: &[i64],
    alignment: u32,
    compute: ComputeDesc,
    algo: i32,
) -> PlanKey

Build a cache key from raw mode/extent slices. Tests that don’t need a live GpuRef use this directly; the dispatch path goes through [build_key_for].