Produce access logs in a binary format

[Keksoj]

For now, access logs are produced by formatting diverse pieces of data, like socket addresses, tags, and so on. std::fmt::Display is implemented for those types, however, calling to_string() on those is CPU-consuming.

It would be beneficiary to produce access logs in a binary format, in order to reduce both formatting time and memory footprint.

Ideally, the binary format would be defined in a protobuf form, like most other types used outside of Sōzu, but this poses the challenge of expressing types like std::net::Socketddr in protobuf.

[Keksoj]

done in #1069