Add option to set a repair callback

[cberner]

This allows the user to abort the repair process and receive progress notifications

Fixes #639

[cberner]

@veryordinally / @raphjaph can you take a look at this API when you get a chance? Will merge it, if it looks like it covers your use case

[casey]

Nice! This works for us. It looks like Self::verify_primary_checksums(mem) is called first, before the repair callback is invoked. Can this take a long time? If so, it would be nice to do a quick check if anything that takes a long time is going to happen, and call repair_callback first if so. Related, if repair_callback is called first, then having progress return 0 for the first call would avoid needing to check if we should skip printing the message, i.e., we could just do if handle.progress() == 0.0 { print_message() }.

[cberner]

I think that's already implemented. It's just in the caller of do_repair. See here: https://github.com/cberner/redb/pull/700/files#diff-7d7d3a6ce5c2a3e8b39ce4f49b78a71365c8e06c0d9ddb78bc2dca68bfeb4a5bR683-R688

[casey]

Ah, okay awesome. Looks good to me!

[cberner]

I would recommend against if handle.progress() == 0.0 though. The API doesn't guarantee that the first call will be with a progress value of 0.0 and I might find some reason to change it in the future. Although that does seem unlikely