feat(prebuilt): Split tool node to individual tool nodes (#5888)

Add option to split tool node to individual nodes. 

Summary:
* User code (specifically streaming) may break if it's relying on the
name of the `tools` node
* The boolean flag in the interface is likely **temporary** (especially
if there are no major breaking changes)
* We'll need to decide if we can get rid of the version in create react
agent. "v1" is not consistent conceptually with a node per tool.

libs/prebuilt/tests/test_react_agent_graph.py

@@ -15,6 +15,11 @@ def tool() -> None:
     ...
 
 
+def tool2() -> None:
+    """Another testing tool."""
+    ...
+
+
 def pre_model_hook() -> None:
     """Pre-model hook."""
     ...
@@ -60,3 +65,33 @@ def test_react_agent_graph_structure(
             f"post_model_hook: {post_model_hook}, "
             f"response_format: {response_format}"
         ) from e
+
+
+@pytest.mark.parametrize("tools", [[], [tool, tool2]], ids=["no_tools", "two_tools"])
+@pytest.mark.parametrize(
+    "pre_model_hook", [None, pre_model_hook], ids=["no_pre_hook", "with_pre_hook"]
+)
+@pytest.mark.parametrize(
+    "post_model_hook", [None, post_model_hook], ids=["no_post_hook", "with_post_hook"]
+)
+@pytest.mark.parametrize(
+    "response_format",
+    [None, ResponseFormat],
+    ids=["no_response_format", "with_response_format"],
+)
+def test_react_agent_graph_structure_with_individual_nodes(
+    snapshot: SnapshotAssertion,
+    tools: list[Callable],
+    pre_model_hook: Union[Callable, None],
+    post_model_hook: Union[Callable, None],
+    response_format: Union[type[BaseModel], None],
+) -> None:
+    agent = create_react_agent(
+        model,
+        tools=tools,
+        pre_model_hook=pre_model_hook,
+        post_model_hook=post_model_hook,
+        response_format=response_format,
+        use_individual_tool_nodes=True,
+    )
+    assert agent.get_graph().draw_mermaid(with_styles=False) == snapshot