chore: code optimization

[lxfu1]

1. 删除 searchHybridSync
2. dead code 清理
3. 类型导出简化
4. 抽取公共哈希函数
5. 删除未使用的 loader

[gemini-code-assist]

Code Review

This pull request refactors the codebase by making the vector store search asynchronous, simplifying the TransformerVectorizer initialization, moving the Loader interface to types, and introducing a centralized generateDocId helper. Feedback on the changes highlights potential ID collisions when using only the file basename for document IDs, the risk of runtime errors from non-null assertions when retrieving documents during queries, and the recommendation to retain the close() method in ZVecStore to properly release file locks in tests.

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