Test pipelining support in pgproto

PostgreSQL supports message pipelining, allowing a client to send multiple messages consecutively without waiting for an acknowledgment. This pipeline is terminated by a Sync message, which enables the server to discard the remaining messages in case of an error and synchronize with the client.

Proposal:

We propose to implement tests to verify that pgproto can correctly process both regular message pipelines and pipelines containing errors. These tests should ensure that:

1. pgproto correctly processes a series of pipelined messages.
2. In the event of an error, pgproto appropriately handles the error and skips the remaining messages up to the Sync message.