Change join_output_by_rowlist_perkey_rows_threshold to unsigned integer

Why it matters

The change ensures that the join_output_by_rowlist_perkey_rows_threshold setting only accepts non-negative values, improving type safety and preventing invalid negative inputs.

How to use it

Users can set the join_output_by_rowlist_perkey_rows_threshold parameter with an unsigned integer value in their configuration or session settings as usual. No other changes in usage are required.