Merge branch 'ps/object-store-midx' into ps/object-store-midx-dedup-info

* ps/object-store-midx: midx: remove now-unused linked list of multi-pack indices packfile: stop using linked MIDX list in `get_all_packs()` packfile: stop using linked MIDX list in `find_pack_entry()` packfile: refactor `get_multi_pack_index()` to work on sources midx: stop using linked list when closing MIDX packfile: refactor `prepare_packed_git_one()` to work on sources midx: start tracking per object database source