Update ToolStreamEvent api to use nested structure

Per PR feedback

Author: zastrowm

src/strands/types/_events.py

@@ -282,12 +282,12 @@ def __init__(self, tool_use: ToolUse, tool_stream_data: Any) -> None:
             tool_use: The tool invocation producing the stream
             tool_stream_data: The yielded event from the tool execution
         """
-        super().__init__({"tool_stream_tool_use": tool_use, "tool_stream_data": tool_stream_data})
+        super().__init__({"tool_stream_event": {"tool_use": tool_use, "data": tool_stream_data}})
 
     @property
     def tool_use_id(self) -> str:
         """The toolUseId associated with this stream."""
-        return cast(str, cast(ToolUse, self.get("tool_stream_tool_use")).get("toolUseId"))
+        return cast(str, cast(ToolUse, self.get("tool_stream_event").get("tool_use")).get("toolUseId"))
 
 
 class ModelMessageEvent(TypedEvent):

tests/strands/agent/hooks/test_agent_events.py

@@ -261,12 +261,16 @@ async def test_stream_e2e_success(alist):
             }
         },
         {
-            "tool_stream_data": {"tool_streaming": True},
-            "tool_stream_tool_use": {"input": {}, "name": "streaming_tool", "toolUseId": "12345"},
+            "tool_stream_event": {
+                "data": {"tool_streaming": True},
+                "tool_use": {"input": {}, "name": "streaming_tool", "toolUseId": "12345"},
+            }
         },
         {
-            "tool_stream_data": "Final result",
-            "tool_stream_tool_use": {"input": {}, "name": "streaming_tool", "toolUseId": "12345"},
+            "tool_stream_event": {
+                "data": "Final result",
+                "tool_use": {"input": {}, "name": "streaming_tool", "toolUseId": "12345"},
+            }
         },
         {
             "message": {