chore: drop Python 3.9 (and syntax) (#6289)

* `strict=False` is the default, pyupgrade to min version 3.10 adds this
to be explicit w/ behavior

libs/prebuilt/tests/test_react_agent.py

@@ -4,12 +4,8 @@ import json
 from functools import partial
 from typing import (
     Annotated,
-    List,
     Literal,
-    Optional,
-    Type,
     TypeVar,
-    Union,
 )
 
 import pytest
@@ -419,7 +415,7 @@ def test__infer_handled_types() -> None:
     def handle2(e: Exception) -> str:
         return ""
 
-    def handle3(e: Union[ValueError, ToolException]) -> str:
+    def handle3(e: ValueError | ToolException) -> str:
         return ""
 
     class Handler:
@@ -428,7 +424,7 @@ def test__infer_handled_types() -> None:
 
     handle4 = Handler().handle
 
-    def handle5(e: Union[Union[TypeError, ValueError], ToolException]):
+    def handle5(e: TypeError | ValueError | ToolException):
         return ""
 
     expected: tuple = (Exception,)
@@ -467,7 +463,7 @@ def test__infer_handled_types() -> None:
 
     with pytest.raises(ValueError):
 
-        def handler(e: Union[str, int]):
+        def handler(e: str | int):
             return ""
 
         _infer_handled_types(handler)
@@ -506,7 +502,7 @@ class CustomState(AgentState):
 
 
 class CustomStatePydantic(AgentStatePydantic):
-    user_name: Optional[str] = None
+    user_name: str | None = None
 
 
 @pytest.mark.parametrize("version", REACT_TOOL_CALL_VERSIONS)
@@ -687,7 +683,7 @@ T = TypeVar("T")
         _InjectedStateDataclassSchema,
     ],
 )
-def test_tool_node_inject_state(schema_: Type[T]) -> None:
+def test_tool_node_inject_state(schema_: type[T]) -> None:
     def tool1(some_val: int, state: Annotated[T, InjectedState]) -> str:
         """Tool 1 docstring."""
         if isinstance(state, dict):
@@ -705,13 +701,13 @@ def test_tool_node_inject_state(schema_: Type[T]) -> None:
     def tool3(
         some_val: int,
         foo: Annotated[str, InjectedState("foo")],
-        msgs: Annotated[List[AnyMessage], InjectedState("messages")],
+        msgs: Annotated[list[AnyMessage], InjectedState("messages")],
     ) -> str:
         """Tool 1 docstring."""
         return foo
 
     def tool4(
-        some_val: int, msgs: Annotated[List[AnyMessage], InjectedState("messages")]
+        some_val: int, msgs: Annotated[list[AnyMessage], InjectedState("messages")]
     ) -> str:
         """Tool 1 docstring."""
         return msgs[0].content
@@ -2012,7 +2008,7 @@ def test_post_model_hook_with_structured_output() -> None:
         flag: bool
         structured_response: WeatherResponse
 
-    def post_model_hook(state: State) -> Union[dict[str, bool], Command]:
+    def post_model_hook(state: State) -> dict[str, bool] | Command:
         return {"flag": True}
 
     agent = create_react_agent(