feat: implement authentication and termination

pgproto/Cargo.lock

pgproto/Cargo.toml

pgproto/examples/demo.lua

pgproto/src/auth.rs

pgproto/src/client.rs

pgproto/src/error.rs

pgproto/src/helpers.rs

pgproto/src/lib.rs

pgproto/src/messages.rs

pgproto/test/auth_test.py

pgproto/test/conftest.py