Quality: Test your decoder using `ByteToMessageDecoderVerifier`

[fabianfett]

I highly recommend testing your message decoder using the ByteToMessageDecoderVerifier. It will test your decoder implementation in multiple ways and ensure that you are doing the right thing. This will improve trust in your library significantly.

Example code: https://github.com/vapor/postgres-nio/blob/c7edb9b71e5055a0c5d918b91a44a88498b997c4/Tests/PostgresNIOTests/New/Messages/RowDescriptionTests.swift