Function collect_changed_submodules_for_fetch 

pub fn collect_changed_submodules_for_fetch(
    repo: &Repository,
    positive_hex: &[String],
    negative_hex: &[String],
) -> Result<Vec<ChangedSubmoduleFetch>>

Walk rev_list(repo, positive_hex, negative_hex) and collect submodule names whose gitlink targets changed, matching Git’s collect_changed_submodules + name resolution.