Merge branch 'ps/odb-source-packed'

The packed object source has been refactored into a proper struct odb_source. * ps/odb-source-packed: odb/source-packed: drop pointer to "files" parent source midx: refactor interfaces to work on "packed" source odb/source-packed: stub out remaining functions odb/source-packed: wire up `freshen_object()` callback odb/source-packed: wire up `find_abbrev_len()` callback odb/source-packed: wire up `count_objects()` callback odb/source-packed: wire up `for_each_object()` callback odb/source-packed: wire up `read_object_stream()` callback odb/source-packed: wire up `read_object_info()` callback packfile: use higher-level interface to implement `has_object_pack()` odb/source-packed: wire up `reprepare()` callback odb/source-packed: wire up `close()` callback odb/source-packed: start converting to a proper `struct odb_source` odb/source-packed: store pointer to "files" instead of generic source packfile: move packed source into "odb/" subsystem packfile: split out packfile list logic packfile: rename `struct packfile_store` to `odb_source_packed`