feat(plugins): introduce middleware token proxy plugin suite (reorder, dedup, lookup, skill index)

[SNM-SNM]

Overview

This PR introduces a suite of Middleware Token Proxy Plugins designed to sit between agent frameworks (e.g., OpenClaw) and LLM engines (e.g., SGLang) to optimize KV cache sharing, minimize context budgets, and perform cache-aware routing.

These modules implement the core optimizations detailed in the MSc cache optimization project (Direction A).

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Key Features

1. Static Context Optimization Plugins (WP1)

• ContextReorderPlugin: Processes OpenAI-formatted request batches to group similar contexts, maximizing RadixAttention prefix sharing on SGLang.
• ContextDedupPlugin: Conversation-aware history compressor. It tracks session turns and automatically replaces redundant historical messages with lightweight reference hints (e.g., [Reference to Turn 1]) utilizing the ConversationTracker.

2. Dynamic Routing & Tool Filtering Plugins (WP2)

• KVCacheLookupPlugin: Subscribes to SGLang worker event streams via ZeroMQ (ZMQ) to build a real-time, in-memory Shadow Radix Tree representing the workers' GPU KV cache. Routes incoming requests to the worker with the longest prefix match.
• SkillAwareContextPlugin: Dynamically filters and injects tool schemas into the request's tools array based on the _required_skills list, trimming unused tool definitions to save context budget.

3. Core Engine Optimizations & Fixes

• Multiprocessing Bypass: Added an execution bypass in compute_distance_cpu.py when num_workers == 1 to eliminate multiprocessing.Pool initialization and IPC serialization overhead.
• Windows Terminal Compatibility: Replaced Unicode checkmark character ✓ with standard + in all logging/printing calls to prevent UnicodeEncodeError crashes on non-UTF-8 consoles.
• Dependencies: Added pytest-asyncio, pyzmq, and msgspec to dependencies to ensure successful integration and testing.

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Verification & Testing

• Mock Proxy Test: Added a complete pipeline mock test in evaluation/core_merge/mock_proxy.py to demonstrate the end-to-end integration and telemetry collection of all four plugins.
• Unit Tests: Added tests/test_kv_lookup.py and tests/test_skill_index.py.
• CI status: All 184 CPU tests passed successfully.