[fel] add key scenario cases

[loveTsong]

🔗 相关问题 / Related Issue

Issue 链接 / Issue Link: #167

• 我已经创建了相关 Issue 并进行了讨论 / I have created and discussed the related issue
• 这是一个微小的修改（如错别字），不需要 Issue / This is a trivial change (like typo fix) that doesn't need an issue

📋 变更类型 / Type of Change

• 🐛 Bug 修复 / Bug fix (non-breaking change which fixes an issue)
• ✨ 新功能 / New feature (non-breaking change which adds functionality)
• 💥 破坏性变更 / Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📚 文档更新 / Documentation update
• 🔧 重构 / Refactoring (no functional changes)
• ⚡ 性能优化 / Performance improvement
• 🧹 代码清理 / Code cleanup

📝 变更目的 / Purpose of the Change

增加关键示例用于突出核心特性

📋 主要变更 / Brief Changelog

• 增加when then的条件分支用法。
• 增加三个示例突出在流式处理、背压和并发的特性。

🧪 验证变更 / Verifying this Change

测试步骤 / Test Steps

1. 运行示例
2. 示例运行全部通过

测试覆盖 / Test Coverage

• 我已经添加了单元测试 / I have added unit tests
• 所有现有测试都通过 / All existing tests pass
• 我已经进行了手动测试 / I have performed manual testing

📸 截图 / Screenshots

✅ 贡献者检查清单 / Contributor Checklist

请确保你的 Pull Request 符合以下要求 / Please ensure your Pull Request meets the following requirements:

基本要求 / Basic Requirements:

• 确保有 GitHub Issue 对应这个变更（微小变更如错别字除外）/ Make sure there is a Github issue filed for the change (trivial changes like typos excluded)
• 你的 Pull Request 只解决一个 Issue，没有包含其他不相关的变更 / Your PR addresses just this issue, without pulling in other changes - one PR resolves one issue
• PR 中的每个 commit 都有有意义的主题行和描述 / Each commit in the PR has a meaningful subject line and body

代码质量 / Code Quality:

• 我的代码遵循项目的代码规范 / My code follows the project's coding standards
• 我已经进行了自我代码审查 / I have performed a self-review of my code
• 我已经为复杂的代码添加了必要的注释 / I have commented my code, particularly in hard-to-understand areas

测试要求 / Testing Requirements:

• 我已经编写了必要的单元测试来验证逻辑正确性 / I have written necessary unit-tests to verify the logic correction
• 当存在跨模块依赖时，我尽量使用了 mock / I have used mocks when cross-module dependencies exist
• 基础检查通过：mvn -B clean package -Dmaven.test.skip=true，elsa README 中的编译检查 / Basic checks pass
• 单元测试通过：mvn clean install / Unit tests pass

文档和兼容性 / Documentation and Compatibility:

• 我已经更新了相应的文档 / I have made corresponding changes to the documentation
• 如果有破坏性变更，我已经在 PR 描述中详细说明 / If there are breaking changes, I have documented them in detail
• 我已经考虑了向后兼容性 / I have considered backward compatibility

📋 附加信息 / Additional Notes

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审查者注意事项 / Reviewer Notes: