Function compose_seed 

pub fn compose_seed(
    workbook_seed: u64,
    sheet_id: u32,
    row: u32,
    col: u32,
    fn_salt: u64,
    recalc_epoch: u64,
) -> (u64, u64)

Compose a deterministic 128-bit seed from components. Returns two u64 lanes suitable to seed SmallRng.