Does COPY FROM gaurentee no partial rows?

Nobody has claimed this yet.

A quick question, since this is not very obvious from the postgres or asyncpg docs: under what circumstances, if any, does `copy_from_query` guarantee that no partial rows will be delivered to the `output` coroutine?

In my experience this hasn't happened, and I could try some more exhaustive testing, but I imagine/hope that someone might just already know the answer.

To me the options seem to be:
- If the networking code reads one line at a time, then the 'text' format guarantees full rows, but not necessarily 'csv' or 'binary'
- Asyncpg itself or postgres itself may explicitly implement such a guarantee?
- Otherwise, there is no guarantee.

Start with the PostgreSQL and asyncpg documentation for copy_from_query, then trace how its output coroutine is described in the available asyncpg material. Document the circumstances, if any, under which text, CSV, and binary output avoid partial rows, and make the guarantee clear to users.

Written by the indexing model from the issue text.