pgproto: pick low-hanging fruits of raw performance

As a starting point of increasing pgproto's performance, we should run a few basic benchmarks, render the flamegraphs and spot the most obvious unnecessary actions which limit the rps.

For instance, it occurred to me that we have otel enabled unconditionally for all bind messages:

https://git.picodata.io/picodata/picodata/picodata/-/blob/5185a147/src/pgproto/backend.rs#L402

In my setup, changing it to false improved the rps from 600 to 750.