Support streaming with pg-native

[segevfiner]

pg-query-strream is not currently supported when using pg-native, which means you can't stream large results sets when using it, it should be supported. libpg does have interfaces to "stream" results https://www.postgresql.org/docs/current/libpq-single-row-mode.html, so it should be possible.

From knex/knex#6295

[charmander]

Not the same type of streaming: pg-query-stream uses cursors.

[segevfiner]

Protocol level streaming is still better then no streaming. What's actually missing from libpq for cursors?