Function generate_biased_walks_precomp_ref_parallel_from_nodes 

pub fn generate_biased_walks_precomp_ref_parallel_from_nodes(
    pre: &PrecomputedBiasedWalks,
    start_nodes: &[usize],
    config: WalkConfig,
) -> Vec<Vec<usize>>

Deterministic parallel precomputed node2vec biased walks (delta/sharded start nodes).

Invariant: output is stable for a fixed seed, independent of Rayon thread count.