libsql: add read your writes support

[LucioFranco]

Fixes #623

[psarna]

To clarify - this is the important bit that gives us read-before-wrote, right? Combined with the fact that writer.replicator is only engaged if we passed read_before_write == true before.

[psarna]

Also, @LucioFranco, res returned from execute_program contains the latest frame number after the program got executed, right? So perhaps it makes sense to make sync_oneshot take a frame_no parameter, and sync just to this specific frame, instead of waiting until we catch up with the primary (so instead of returning from sync_oneshot when replica_index >= primary_index, we'd return when replica_index >= that_index_we_just_received_in_the_response_above)? If I understand correctly, it could make read-your-writes more leightweight, because we'd only wait for our write, not potentially somebody else's.

[LucioFranco]

Sure, lets do this in a follow up 👍