Merge branch 'jt/pack-objects-prefetch-in-batch'

While packing many objects in a repository with a promissor remote, lazily fetching missing objects from the promissor remote one by one may be inefficient---the code now attempts to fetch all the missing objects in batch (obviously this won't work for a lazy clone that lazily fetches tree objects as you cannot even enumerate what blobs are missing until you learn which trees are missing). * jt/pack-objects-prefetch-in-batch: pack-objects: prefetch objects to be packed pack-objects: refactor to oid_object_info_extended