Apply recommendations from duckdb to improve speed

DuckDB has a dedicated page called "My Workload Is Slow"

https://duckdb.org/docs/guides/performance/my_workload_is_slow

and more generally all the https://duckdb.org/docs/guides/performance/overview section.

It could be good to review if some recommendations apply to our usage of duckdb.

Start with DuckDB's "My Workload Is Slow" guide and the performance overview linked in the issue, then inspect how this repository uses DuckDB. Done means identifying applicable recommendations, applying the relevant changes, and demonstrating that they improve speed.

Written by the indexing model from the issue text.