Add Bluesky team's interop test cases

[snarfed]

@bnewbold mentioned that they have some repo interop test cases in their open source projects. We should add them here! bluesky-social/atproto#2644 (comment) :

There are some interop test cases in each of these implementations. The two most basic types of validation tests are full repositories (CAR files) and very simple repo layouts (a set of records and paths). The tests basically read in the repo (from CAR file or description) in to an array or some other simple data structure; and then re-produce / re-export the repo, and validate that the shape and data hashes all match up. I very strongly recommend that anybody working on an MST/repo implementation both write their own tests as they work (both unit and integration tests), and then copy in these exact interop tests to cover the known tricky cases.