fix: fix n8n streaming support issue

[myml]

概述 / Overview

请在此部分填写你实现/解决/优化的内容:
Summary of what you implemented/solved/optimized:

Add streaming support detection and proper message type handling for n8n service API runner. Previously, when streaming was enabled, n8n integration would fail due to incorrect message type usage.

1. Added streaming capability detection by checking adapter's is_stream_output_supported method
2. Implemented conditional message generation using MessageChunk for streaming mode and Message for non-streaming mode
3. Added proper error handling for adapters that don't support streaming detection

Fixed #1777

检查清单 / Checklist

PR 作者完成 / For PR author

请在方括号间写x以打勾 / Please tick the box with x

• 阅读仓库贡献指引了吗？ / Have you read the contribution guide?
• 与项目所有者沟通过了吗？ / Have you communicated with the project maintainer?
• 我确定已自行测试所作的更改，确保功能符合预期。 / I have tested the changes and ensured they work as expected.

项目维护者完成 / For project maintainer

• 相关 issues 链接了吗？ / Have you linked the related issues?
• 配置项写好了吗？迁移写好了吗？生效了吗？ / Have you written the configuration items? Have you written the migration? Has it taken effect?
• 依赖加到 pyproject.toml 和 core/bootutils/deps.py 了吗 / Have you added the dependencies to pyproject.toml and core/bootutils/deps.py?
• 文档编写了吗？ / Have you written the documentation?

[Copilot]

Pull Request Overview

This PR adds streaming support detection and proper message type handling for the n8n service API runner to prevent failures when streaming is enabled.

• Implemented streaming capability detection using the adapter's is_stream_output_supported() method
• Added conditional message generation using MessageChunk for streaming mode and Message for non-streaming mode
• Included error handling for adapters that don't support streaming detection

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[fdc310]

@myml 我这边针对n8n的流式工作流做了一部分的修改，你看一下（我不知道为啥用不了原非流式的那种，你可以看看测一下有没有影响），关于流式工作流的配置可以参考一下langbot_wiki的分支n8n_docs

[RockChinQ]

https://docs.langbot.app/zh/deploy/pipelines/n8n.html master已更新，可以按照这个文档配置一下n8n流式