Function is_collected 

async fn is_collected(
    catalog: &RwLock<ObjectCatalog>,
    deleting: &DeletingObjects,
    object_seq: u64,
) -> bool

Returns whether collection deleted the object object_seq after a read listed it. The set of deleting objects is observed before the catalog, the reverse of the order the actor updates them, so an object that no longer looks deleting but still looks indexed was never collected. An undecided delete is waited for.