refactor: complete migration to native Python typing

- Replace Union[A, B] with A | B (using string literals for forward refs)
- Replace Optional[T] with T | None
- Replace List[T] with list[T]
- Replace Any with any
- Use collections.abc.Callable instead of typing.Callable
- Maintain TYPE_CHECKING for circular import resolution
- All tests pass with native typing syntax

🤖 Assisted by Amazon Q Developer

Author: mrlee-amazon

src/strands/experimental/agent_config.py

@@ -45,7 +45,7 @@ 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) -> "Agent":
         """Create an Agent instance from this configuration.
         
         Args:

src/strands/experimental/tool_pool.py

@@ -2,7 +2,7 @@
 # ABOUTME: Integrates with existing tool infrastructure and @tool decorator pattern
 """Experimental tool pool system for structured tool management."""
 
-from typing import Any, Optional, Union, Callable
+from collections.abc import Callable
 
 from ..types.tools import AgentTool
 from ..tools.tools import PythonAgentTool
@@ -12,7 +12,7 @@
 class ToolPool:
     """Pool of available tools for agent selection using existing tool infrastructure."""
 
-    def __init__(self, tools: Optional[list[Union[AgentTool, Callable]]] = None):
+    def __init__(self, tools: "list[AgentTool | Callable] | None" = None):
         """Initialize tool pool.
         
         Args:
@@ -56,7 +56,7 @@ def add_tool_function(self, tool_func: Callable) -> None:
         else:
             raise ValueError(f"Function {tool_func.__name__} is not decorated with @tool")
 
-    def add_tools_from_module(self, module: Any) -> None:
+    def add_tools_from_module(self, module: any) -> None:
         """Add all @tool decorated functions from a Python module.
         
         Args:
@@ -69,7 +69,7 @@ def add_tools_from_module(self, module: Any) -> None:
                 self.add_tool_function(obj)
 
     @classmethod
-    def from_module(cls, module: Any) -> "ToolPool":
+    def from_module(cls, module: any) -> "ToolPool":
         """Create ToolPool from all @tool functions in a module.
         
         Args:
@@ -82,7 +82,7 @@ def from_module(cls, module: Any) -> "ToolPool":
         pool.add_tools_from_module(module)
         return pool
 
-    def get_tool(self, name: str) -> Optional[AgentTool]:
+    def get_tool(self, name: str) -> AgentTool | None:
         """Get tool by name.
         
         Args: