FSCK in gitoxide-core

[Byron]

Essentially a verify_integrity() on git_odb::Store, run integrity checks on all indices/multi-indices and summarize the results.

• multi-index verification #282
• rough FSCK for git-odb::Store #290
• More flags for CLI to fully configure traversal - turns out there are always packs with ref-deltas unfortunately and mention in the CLI
• Fix this to allow it to work with these pesci ref-delta packs which seem to be produced by GitHub right now.