Only bootstrap a compact range once per log

As opposed to doing a new bootstrap with get-proof-by-hash every time the next root is constructed. Bootstrapping the compact range from a get-proof-by-hash query works for the most part, but fails if the log included a duplicate entry and gives us the index for that instead. Log operators with duplicate entries include Cloudflare and Digicert.

If bootstrap fails (unlucky), we try to bootstrap again once the log's signed tree head moved forward (hoping the last entry has no duplicate).

The more reliable way to bootstrap a compact range would be to use the get-entry-and-proof endpoint. This does not work in practise because some logs are not implementing this endpoint. Digicert has such logs.