add open property to Connection to ensure maintenance of existing API

Signed-off-by: varun-edachali-dbx <varun.edachali@databricks.com>

Author: varun-edachali-dbx

src/databricks/sql/client.py

@@ -346,9 +346,7 @@ def get_protocol_version(openSessionResp):
     @property
     def open(self) -> bool:
         """Return whether the connection is open by checking if the session is open."""
-        # NOTE: we have to check for the existence of session in case the __del__ is called
-        # before the session is instantiated
-        return hasattr(self, "session") and self.session.open
+        return self.session.open
 
     def cursor(
         self,