fix: remove live event buffering in runner

[wuliang229]

Keep the ADK events in their original order as they arrive. In the original code, if the output transcriptions are long, the function call and response events are only appended at the very end of transcription. If any downstream program consumes the events, they are in the wrong order.

[adk-bot]

Response from ADK Triaging Agent

Hello @wuliang229, thank you for creating this PR!

To help us review your PR more efficiently and ensure it aligns with our contribution guidelines, could you please update the PR description to include the following:

1. Testing Plan: Please include a testing plan section describing how you tested these changes (e.g., unit tests run or manual E2E verification).
2. Logs or Screenshots: Since this is a bug fix related to event ordering in the runner, providing logs or a screenshot showing the correct event sequence after applying the fix would be extremely helpful.
3. Issue Association: If there is an associated GitHub issue for this fix, please reference/link it in the PR description.

For more details on these requirements, please consult our Contribution Guidelines.

Thank you!