Add support for multiple Agent Frameworks

[destroyersrt]

Add Modular Support for Multiple Agent Frameworks and LLM Providers

Description

Implement a modular architecture to support multiple agent frameworks (LangChain, CrewAI, AutoGen) and LLM providers (OpenAI, Anthropic, Gemini) through a plugin-based system. This allows users to build agents using their preferred framework and LLM while maintaining interoperability through NEST's protocol layer.

Implementation Approach

• Create AgentFramework abstract interface for framework adapters
• Create LLMProvider abstract interface for model providers
• Implement framework adapters: LangChainAdapter, CrewAIAdapter, AutoGenAdapter
• Implement LLM provider adapters: OpenAIProvider, AnthropicProvider, GeminiProvider
• Config-driven framework and provider selection
• Framework adapters bridge to NEST's protocol router (SLIM/A2A)

Acceptance Criteria

• AgentFramework abstract base class with initialize(), process_message(), get_capabilities() methods
• LLMProvider abstract base class with generate(), stream(), get_models() methods
• LangChain, CrewAI, AutoGen framework adapters implemented
• OpenAI, Anthropic, Gemini provider adapters implemented
• Config allows specifying framework and provider: agent.framework, agent.llm_provider, agent.model
• Framework adapters integrate with protocol router for inter-agent communication
• Agents built with different frameworks can communicate via common protocols
• Support for framework-specific features (LangChain tools, CrewAI roles, AutoGen conversations)
• Documentation for adding custom framework/provider adapters
• Tests for each framework and provider adapter