[Feature] Return the rows affected in the adapter response

[rchui]

Other DBT adapters return in their response a field containing the "rows affected" and outputs a log like: [0 1 OK] to indicate the number of rows that were affected by an incremental / table model. This information is useful because these metrics can be harvested to track pipeline throughput and monitor for performance regressions.

It would be useful if dbt-duckdb also returned this.

[jwills]

Ah yeah I wanted this back in the day when I first started working on the adapter, but IIRC the DuckDB python API didn't support it (i.e., it doesn't actually return the counts of affected rows for the statement via the rowcount field on the cursor object, it's just always -1.

I just tried it out on 1.1.3 and confirmed that it's still the case, and I don't think it's something that is easily fixable in DuckDB itself, see: duckdb/duckdb#7924