Feature Request: Add a "duckdb.force_execution" that fails execution if DuckDB cannot be used

[ggam-tsbtrans]

Currently you can request DuckDB execution via duckdb.force_execution=true. But it will fallback to Postgres if DuckDB cannot be used (for example #917).

This is the best behaviour in production, but it's not so useful when you're specifically trying to debug some query and make sure DuckDB is used.

I propose a setting like duckdb.fail_query_if_incompatible_with_duckdb=true, only configurable at session level, that fails queries that couldn't be executed with DuckDB.