fix: VikingDB volcengine URI prefix loss and stale is_leaf filter

[qin-ctx]

Description

修复 VikingDB volcengine 后端的两个 bug 以及 S3 后端的一个 bug：

1. 读取记录时 URI viking:// 前缀丢失，导致 Access Denied
2. memory_deduplicator.py 中残留已废弃的 is_leaf 字段过滤（PR feat: break change, remove is_leaf scalar and use level instead #271 遗漏）
3. S3 目录 rename 只移动单个文件，未处理整个子目录树

Related Issue

Fixes #288

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

• 在 VikingVectorIndexBackend 中添加 _restore_uri_fields() 静态方法，在读取记录时还原 uri/parent_uri 字段的 viking:// 前缀。在 get()、fetch_by_uri()、search()、filter() 四个出口处调用，scroll() 和 _remove_descendants() 经由 filter() 间接覆盖。幂等操作，对 local/http 后端无副作用。
• 将 memory_deduplicator.py 中 {"field": "is_leaf", "op": "must", "conds": [True]} 替换为 {"field": "level", "op": "must", "conds": [2]}，与 PR feat: break change, remove is_leaf scalar and use level instead #271 的 schema 变更对齐。
• S3 client 新增 CopyObject() 和 ListAllObjects() 方法；重构 s3fs.Rename() 支持目录级别的移动，通过服务端 copy + delete 递归处理整个子目录树。

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)

N/A

Additional Notes

• _restore_uri_fields() 是 volcengine_collection._sanitize_uri_value() 的逆操作：去除首尾 / 后加上 viking:// 前缀。通过 not val.startswith("viking://") 保证对 local/http 后端幂等安全。

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