Fix Engine and OpenAI Agents adapter

[jakeloo]

This pull request includes several updates to the Thirdweb AI services and examples, with a focus on enhancing the Engine service and improving schema handling. The most important changes include adding new functionalities to the Engine service, updating the example script to use the new Engine service, and improving schema parsing in the OpenAI adapter.

Enhancements to the Engine service:

• python/thirdweb-ai/src/thirdweb_ai/services/engine.py: Added _make_headers method to include Authorization and X-Backend-Wallet-Address headers if available. Updated various methods to include chain_id and backend_wallet_address parameters and adjusted payload handling. [1] [2] [3] [4] [5] [6]

Updates to the example script:

• python/examples/adapter_openai/example.py: Imported the Engine class and initialized it with environment variables. Updated the Agent initialization to include tools from the Engine instance. [1] [2]

Improvements to schema handling:

• python/thirdweb-ai/src/thirdweb_ai/adapters/openai/agents.py: Enhanced _get_openai_schema function to recursively handle anyOf, oneOf, and allOf fields in schemas.

General codebase improvements:

• python/thirdweb-ai/src/thirdweb_ai/services/service.py: Refactored _get and _post methods to ensure base URLs are properly formatted and headers are merged correctly.