I want to implement streaming results in DuckDB.NET library, similar to result streaming in JDBC. For this I need a streaming duckdb_result

Using the C Api the only to get a streaming result is with Pending Result Interface but it has an awkward API, (it requires calling duckdb_pending_execute_task in a loop and polling with duckdb_pending_execution_is_finished)

I propose you add a new API that takes a prepared_statement and creates a streaming result. It can look like this:

duckdb_state duckdb_execute_prepared_streaming(
  duckdb_prepared_statement prepared_statement,
  duckdb_result *out_result
);