Function num_splits 

pub fn num_splits(
    policy: SplitkPolicy,
    sm_count: u32,
    num_q_heads: u32,
    legacy_ref_seqs: u32,
) -> u32

The split count for a launch.

⚠️ legacy_ref_seqs is read by SplitkPolicy::Legacy ONLY. Every other arm is a pure function of configuration, which is the determinism invariant this module exists to hold — see the module header, and the_auto_split_count_does_not_move_with_the_co_batched_count.