feat(integrations): add OneBot v11 adapter for NapCat/QQ bot integration

[h0ll0w-AkuZr0guY]

📝 Pull Request Summary

Adds an integration adapter for the OneBot v11 protocol, enabling memU to act as the long-term memory engine for QQ bots (via implementations like NapCatQQ).

Fixes #367

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✅ What does this PR do?

• Introduces OneBotAdapter and OneBotConfig in src/memu/integrations/onebot.py.
• Implements a resilient WebSocket client with automatic reconnection and heartbeat capabilities.
• Handles Promise/Echo mechanisms for robust asynchronous message sending (_send_with_response).
• Adds a comprehensive example script demonstrating how to connect NapCatQQ with memU's RAG pipeline (examples/onebot_demo.py).

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🤔 Why is this change needed?

• Platform Expansion: Expanding support to QQ (via OneBot) allows millions of users to utilize memU in highly active community groups and personal assistant scenarios.
• Resilience: The native Python websockets implementation often clashes with CQHTTP/NapCat's heartbeat. This adapter correctly handles silent pings and auto-reconnects, ensuring 24/7 stability.

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🔍 Type of Change

Please check what applies:

• Bug fix
• New feature
• Documentation update
• Refactor / cleanup
• Other (please explain)

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✅ PR Quality Checklist

• PR title follows the conventional format (feat:, fix:, docs:)
• Changes are limited in scope and easy to review
• Documentation updated where applicable
• No breaking changes (or clearly documented)
• Related issues or discussions linked

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📌 Optional

• Tested locally with a live NapCatQQ instance and Qwen/BGE-M3 models. User-specific long-term memory recall functions flawlessly across different QQ accounts.