* Light client on-demand request for headers range.
* Cache headers in HeaderWithAncestors response.
Also fulfills request locally if all headers are in cache.
* LightFetch::logs fetches missing headers on demand.
* LightFetch::logs limit the number of headers requested at a time.
* LightFetch::logs refactor header fetching logic.
* Enforce limit on header range length in light client logs request.
* Fix light request tests after struct change.
* Respond to review comments.
9ed43230ca