fix(python): Ensure that read_database takes advantage of Arrow ret…

…urn from a `duckdb_engine` connection when using a SQLAlchemy `Selectable` (#19255)

py-polars/polars/io/database/_executor.py

@@ -392,7 +392,7 @@ def _normalise_cursor(self, conn: Any) -> Cursor:
                     return conn.engine.raw_connection().cursor()
                 elif conn.engine.driver == "duckdb_engine":
                     self.driver_name = "duckdb"
-                    return conn.engine.raw_connection().driver_connection
+                    return conn
                 elif self._is_alchemy_engine(conn):
                     # note: if we create it, we can close it
                     self.can_close_cursor = True
@@ -505,8 +505,11 @@ def execute(
             )
             result = cursor_execute(query, *positional_options)
 
-        # note: some cursors execute in-place
+        # note: some cursors execute in-place, some access results via a property
         result = self.cursor if result is None else result
+        if self.driver_name == "duckdb":
+            result = result.cursor
+
         self.result = result
         return self