midx: ignore cruft pack with `repack`, `expire`

This series fixes a pair of bugs that were originally pointed out by Gregory Szorc in [1].

Namely, that both git multi-pack-index repack and git multi-pack-index expire can cause us to "absorb" the cruft pack, distributing its objects into a new pack, and removing its metadata.

This is worth avoiding, since even though it doesn't result in object corruption, this bug removes semi-important metadata contained in the .mtimes file, which controls how fast objects leave the repository during a pruning GC.

This series teaches both sub-commands to avoid any cruft pack(s), preserving their metadata.

Thanks in advance for your review.

[1]: https://lore.kernel.org/git/CAKQoGanPBec6wRO6uWrETaoJXdszpjRWytXaJwx6jw0mrrj-gQ@mail.gmail.com/

Taylor Blau (7):
Documentation/git-multi-pack-index.txt: fix typo Documentation/git-multi-pack-index.txt: clarify expire behavior midx.c: prevent expire from removing the cruft pack midx.c: avoid cruft packs with repack --batch-size=0 midx.c: replace xcalloc() with CALLOC_ARRAY() midx.c: remove unnecessary loop condition
midx.c: avoid cruft packs with non-zero repack --batch-size

 Documentation/git-multi-pack-index.txt |  7 +-
 midx.c                                 | 12 +++-
 t/t5319-multi-pack-index.sh            | 94 ++++++++++++++++++++++++++
 3 files changed, 107 insertions(+), 6 deletions(-)

2.37.0.1.g1379af2e9d