utreexoserver: bridgeserver is too slow to serve blocks&proofs

[kcalvinalvin]

The current bridgeserver being too slow to serve blocks has been a problem for forever. This below screenshots show that the client here is spending 37% of the time fetching blocks. Since most of that time is spent on syscalls, it's safe to assume that the client is just waiting for blocks from the server.

This raises the importance of PR #262 (as a performance boost as well as a refactor) as that codebase didn't have this problem of the server being too slow.