feat(providers): create modular provider package structure

[devin-ai-integration]

Refactor: Create providers package to modularize LLM client implementations

This PR addresses issue #1532 by implementing a modular provider package structure for the instructor library. The approach is minimally invasive, moving only the OpenAI provider as an example while maintaining full backward compatibility.

Changes

• Created a new providers/ package with:
  • base.py - Base provider interface
  • openai.py - OpenAI provider implementation
  • __init__.py - Provider registry and exports
• Updated imports in __init__.py and auto_client.py to use the new structure
• Added deprecation warning to existing from_openai function in client.py
• Updated README with migration guide

Implementation Details

This implementation follows the structure proposed in issue #1532:

• providers/base.py contains the base provider interface
• providers/openai.py contains the moved OpenAI implementation
• providers/__init__.py exports the provider functions
• Full backward compatibility is maintained through import forwarding and deprecation warnings

Testing

The implementation maintains backward compatibility:

• from instructor import from_openai still works (with deprecation warning)
• from instructor.providers.openai import from_openai works without warning
• instructor.from_provider("openai/gpt-4") works correctly

TODO

Future work will involve moving the remaining providers to the new structure:

• Anthropic
• Google
• Mistral
• Cohere
• Perplexity
• Groq
• Writer
• Bedrock
• Cerebras
• Fireworks
• VertexAI

Link to Devin run

https://app.devin.ai/sessions/8cb6cdfb710c4442a68796becb4d25ec

This PR was requested by Jason Liu (work@jxnl.co)

[devin-ai-integration]

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