Add proof generation to sequencer

[rozbb]

I found the smallest version of what I need for transparency: it should always be possible for a sequencer (that's been initialized) to produce 1) an inclusion proof for the last leaf, and 2) a consistency proof between the current tree and the current tree minus the last leaf. This PR implements those. I also ran the ignored test to make sure there are no cases where these proofs require hashes that aren't in the edge tiles.

I also made some assorted other fixes:

1. I removed the generic log's check that the checkpoint extension is empty. We use extensions in WAICT.
2. I renamed ctlog.rs in the generic log worker to log_ops.rs, because that's the closest description to what the file does imo

[lukevalenta]

Looks good!