Merge branch 'ps/packfile-store-in-odb-source' into ps/odb-for-each-object

* ps/packfile-store-in-odb-source: packfile: move MIDX into packfile store packfile: refactor `find_pack_entry()` to work on the packfile store packfile: inline `find_kept_pack_entry()` packfile: only prepare owning store in `packfile_store_prepare()` packfile: only prepare owning store in `packfile_store_get_packs()` packfile: move packfile store into object source packfile: refactor misleading code when unusing pack windows packfile: refactor kept-pack cache to work with packfile stores packfile: pass source to `prepare_pack()` packfile: create store via its owning source odb: properly close sources before freeing them builtin/gc: fix condition for whether to write commit graphs