The PostgreSQL server will reject messages greater than ~1 GB anyway.
However, worse than that is that a message that is larger than 4 GB
could wrap the 32-bit integer message size and be interpreted by the
server as multiple messages. This could allow a malicious client to
inject arbitrary protocol messages.
https://github.com/jackc/pgx/security/advisories/GHSA-mrww-27vc-gghv
Use an internal buffer in pgproto3.Frontend and pgproto3.Backend instead
of directly writing to the underlying net.Conn. This will allow tracing
messages as well as simplify pipeline mode.
