Function write_fetch_request_iter 

pub fn write_fetch_request_iter(
    wants: impl Iterator<Item = ObjectId> + Clone,
    options: FetchOptions,
    output: &mut impl Write,
) -> Result<()>

Encode a cloneable iterator of IDs, avoiding temporary ID arrays in adapters. Duplicate probes reread the iterator; it must yield the same IDs on every clone. All wants use one format. Validation precedes any output.