Fix module declarations and compile

[kalisam]

Summary

• hook up DHT module to existing sharding implementation
• remove unused fl_core and vector_db modules
• add missing module files for federated code
• adjust hashing logic in Query and fix cache error handling
• derive Clone for knowledge structs
• disable integration features in the library for now
• add lru crate and ensure build passes

Testing

• cargo check

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https://chatgpt.com/codex/tasks/task_e_6869e1ea4e588331a95a0782deb9a0c7