fix(streaming): add future annotations import to activities

Author: vkalmathscale

src/agentex/lib/core/temporal/plugins/openai_agents/hooks/activities.py

@@ -4,6 +4,8 @@
 to the AgentEx UI, designed to work with TemporalStreamingHooks.
 """
 
+from __future__ import annotations
+
 from typing import Any, Dict
 
 from temporalio import activity