feat: add OpenAI SDK and LangChain framework adapters, implement mnem…

[Arjxm]

This pull request adds support for the OpenAI SDK as a framework adapter alongside existing LangChain integration. It introduces a new OpenAIAdapter for creating and handling tools in the OpenAI function calling format, updates documentation and import logic, and provides detailed examples for both LangChain and OpenAI SDK usage. The changes improve the framework's flexibility and interoperability with modern agent ecosystems.

Framework support and adapters:

• Added a new OpenAIAdapter class in agentarc/frameworks/openai_sdk.py to enable OpenAI SDK function calling integration, including tool schema creation, handler functions, and tool call processing.
• Updated imports and exports in agentarc/__init__.py and agentarc/frameworks/__init__.py to include OpenAIAdapter, with fallback handling for missing dependencies. [1] [2] [3] [4]

Documentation and usage examples:

• Enhanced documentation in agentarc/frameworks/__init__.py to reflect OpenAI SDK support, and provided code examples for both LangChain and OpenAI SDK adapters.
• Updated the main package docstring to list OpenAI SDK as a supported framework.

LangChain improvements:

• Added a new LangChainAdapter implementation in agentarc/frameworks/langchain.py with methods to create structured tools for transactions, balance checks, and wallet info, along with usage examples.…onic and private key wallet adapters, and create example chat agents with policy enforcement