feat(rev_store): store references for tip negotiation

[Alizter]

We now store refs of fetched commits to aid later negotiation.

• Fix Dune fetches full git history on every fetch #13323

See doc/dev/rev-store.md in this PR for a detailed explanation of the mechanism.

[shym]

I confirm that this solves the issue for me, thanks!
Compared to an implementation that would use an explicit --negotiation-tip= using the last fetch from that repository, I understand we gain possibly if some repositories share some history but I wonder about the longer-term performance cost and the privacy leak due to negotiating with all the tips of all the repos we’ve pulled from (I’m not sure how to evaluate them, though).

[Alizter]

Hmm I suppose you are right. Currently we send all the tips, even if they aren't direct related to the remote. I suppose we could improve this by restricting the tips per remote and passing a glob to git. This won't be a shell expansion but should be something that git knows how to interpret without having to choose the exact tips ourselves. This is probably something I can handle in a follow up to this PR however.

[Alizter]

@shym I've opened #13671 to track this concern.