fix: fix agfs-server for windows

[kkkwjx07]

Description

Related Issue

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

fix: 修复 AGFS Server 在 Windows 环境下的路径兼容性问题                                                         
                                                                                                                
主要变更：                                                                                                      
1. 路径处理标准化：在 VFS 核心逻辑（pathutil, handlers, queuefs）中将 `path/filepath` 替换为 `path`             

包，强制使用正斜杠 /，避免 Windows 反斜杠导致的路径解析错误。
2. LocalFS 适配：在 LocalFS 插件中引入
filepath.FromSlash，将虚拟文件系统的正斜杠路径正确转换为当前操作系统的本地路径格式。
3. 清理代码：删除了废弃的测试文件 tests/vectordb/test_serializable.py。

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

Additional Notes

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