Defines the mode of streaming:
- "values": Stream only the values.
- "messages": Stream complete messages.
- "updates": Stream updates to the state.
- "events": Stream events occurring during execution.
- "checkpoints": Stream checkpoints as they are created.
- "tasks": Stream task start and finish events.
- "debug": Stream detailed debug information.
- "custom": Stream custom events.
- "tools": Stream tool events:
on_tool_start, on_tool_event, on_tool_end and on_tool_error.
- "lifecycle": Stream an event when each subgraph starts and ends, with the id of the tool call that started it.
