c/driver/postgresql: investigate performance

### What feature or improvement would you like to see?

https://iangow.github.io/notes/db2pq_test/local_engine_benchmark.html

I don't expect we can win against pg_parquet, but it may be interesting to see how close we can get to DuckDB's extension. IIRC, DuckDB's extension pulls some tricks using internals to parallelize queries, which may not be what we want to do. But we should see if there's any opportunity to squeeze performance.