refactor: remove TYPE_CHECKING dependency for circular imports

- Remove typing.TYPE_CHECKING import and usage
- Use runtime import only where needed (in toAgent method)
- Remove return type annotation to avoid forward reference issues
- Cleaner approach without typing module dependencies
- All tests continue to pass

🤖 Assisted by Amazon Q Developer

Author: mrlee-amazon

src/strands/experimental/agent_config.py

@@ -3,12 +3,6 @@
 """Experimental agent configuration with enhanced instantiation patterns."""
 
 import json
-from typing import TYPE_CHECKING
-
-# Avoid circular import: experimental/agent_config.py -> agent.agent -> 
-# event_loop.event_loop -> experimental.hooks -> experimental.__init__.py -> AgentConfig
-if TYPE_CHECKING:
-    from ..agent.agent import Agent
 
 
 class AgentConfig:
@@ -45,7 +39,7 @@ def tool_pool(self) -> "ToolPool":
         """
         return self._tool_pool
 
-    def toAgent(self, tools: "ToolPool | None" = None, **kwargs: any) -> "Agent":
+    def toAgent(self, tools: "ToolPool | None" = None, **kwargs: any):
         """Create an Agent instance from this configuration.
         
         Args: