Function split_bin 

pub fn split_bin(
    exploded: &Exploded,
    max_loc: usize,
    root_stem: &str,
) -> SplitOutput

Plan and reassemble a binary crate-root split so that every output file is < max_loc. The item budget reserves the full header LOC and the per-part overhead; since a part now copies only the imports it references (a subset of the header), this reservation is conservative — a packed part stays safely under budget.