Alternative cache backends

[dimo414]

Today bkt caches data on disk using a hand-spun "database" on top of the file system. This works reasonably well, but there might be performance / stability / compatibility improvements to be had with a different backend, such as an embedded database like SQLite or RocksDB. Library users might want an in-memory cache as well.

I don't have a clear motivating use case presently, so I'm likely only going to implement these alternative backends for fun when I make time. Please weigh in here if you have a specific use case.