feat: Rename ai proxy enhanced module to ai proxy and update related files

[Aias00]

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[Copilot]

Pull request overview

This pull request renames the "ai-proxy-enhanced" module to "ai-proxy", along with introducing comprehensive implementations of AI proxy functionality including configuration management, caching, retry logic, and fallback mechanisms. The PR adds approximately 1,900 lines of new production code and 1,000 lines of test code.

Key Changes

• Renamed module from shenyu-plugin-ai-proxy-enhanced to shenyu-plugin-ai-proxy in the parent POM
• Implemented core AI proxy plugin with support for streaming and non-streaming requests, dynamic and admin-configured fallbacks, and proxy API key validation
• Added comprehensive caching mechanisms for chat clients and API key mappings with configurable size limits and eviction strategies
• Introduced retry logic with exponential backoff for transient failures and fallback support for non-transient errors

Reviewed changes

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Show a summary per file

File	Description
pom.xml (parent)	Updated module reference from shenyu-plugin-ai-proxy-enhanced to shenyu-plugin-ai-proxy
shenyu-plugin-ai-proxy/pom.xml	New module POM with dependencies on Spring AI, reactor, and testing frameworks
AiProxyPlugin.java	Main plugin implementation handling request routing, configuration resolution, proxy key validation, and streaming/non-streaming responses
AiProxyPluginHandler.java	Plugin data handler managing selector-level configuration and cache invalidation
AiProxyConfigService.java	Service for resolving primary and fallback configurations from global, selector, and request-level sources
AiProxyExecutorService.java	Execution service implementing retry logic with backoff and fallback strategies for AI calls
ChatClientCache.java	Thread-safe cache for ChatClient instances with size-based eviction
AiProxyApiKeyCache.java	Singleton cache for proxy-to-real API key mappings with selector-based invalidation
CommonAiProxyApiKeyDataSubscriber.java	Subscriber implementation for handling API key data updates and cache synchronization
Test files (5 classes)	Comprehensive unit tests covering success scenarios, error handling, edge cases, and null safety

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