fix: handle set_isolation_level gracefully

Whenever the sqlachemy tries to use set_isolation_level without it being defined it will cast `object has no attribute 'set_isolation_level'` instead of gracefully handling the error by explicitly raising it is not implemented.

Author: caiohamamura

duckdb_engine/__init__.py

@@ -330,6 +330,9 @@ def _get_server_version_info(self, connection: "Connection") -> Tuple[int, int]:
     def get_default_isolation_level(self, connection: "Connection") -> None:
         raise NotImplementedError()
 
+    def set_isolation_level(self, connection: "Connection", level: str) -> None:
+        raise NotImplementedError()
+
     def do_rollback(self, connection: "Connection") -> None:
         try:
             super().do_rollback(connection)