Function decide_persistent_kernel 

pub fn decide_persistent_kernel(
    inputs: PersistentKernelInputs,
) -> PersistentKernelDecision

Decide whether to use persistent kernel mode for this batch.

Standard launches cost: batch_size * per_launch_overhead + batch_size * per_item_kernel. Persistent cost: persistent_setup + batch_size * per_item_kernel. Persistent wins iff batch_size * per_launch_overhead > persistent_setup.

Returns StandardLaunches when batch_size is 0 or 1 (persistent mode never wins for a single launch - the setup cost dominates).