Handle rate limit case where there's an update record

[kwannoel]

Credit @stdrc for finding this.

Consider case where rate_limit=1. Then we have an update record. That corresponds to 2 rows.
In such a scenario we need to just emit the entire chunk.

                    let n = NonZeroU32::new(chunk.cardinality() as u32).unwrap();
                    // Ditto.
                    limiter.until_n_ready(n).await.unwrap();

TODO(kwannoel): Also test the append record code, to make sure that the update record is not split on calling StreamChunk::split / DataChunk::split.