fix(community): Handle AIMessage.tool_calls and AIMessageChunk.tool_call_chunks for LangChain 1.0 compatibility

[Madhuram99]

Description

Fixes the OpenAI message adapters to properly handle tool calls in LangChain 1.0+. The adapters were only checking additional_kwargs for tool call information, but LangChain 1.0 moved tool calls to dedicated attributes (tool_calls and tool_call_chunks), causing tool calls to be silently dropped during conversion.

This PR updates the conversion functions to check the new attributes first, then fall back to additional_kwargs for backward compatibility with pre-1.0 versions.

Changes made:

1. convert_message_to_dict() - Now checks AIMessage.tool_calls attribute before additional_kwargs
2. _convert_message_chunk() - Now checks AIMessageChunk.tool_call_chunks attribute before additional_kwargs

Both functions maintain 100% backward compatibility with pre-1.0 LangChain versions.

Closes #414

Issue

Fixes #414 - OpenAI message adapters missing implementation for AIMessage.tool_calls

Dependencies

No new dependencies added.

Testing

Added comprehensive test suite with 36 tests covering:

• AIMessage with tool_calls attribute (LangChain 1.0+)
• AIMessageChunk with tool_call_chunks attribute (streaming, LangChain 1.0+)
• Backward compatibility with additional_kwargs (pre-1.0)
• All message types (Human, System, AI, Function, Tool, Chat)
• Edge cases (empty content, multiple tools, missing fields)
• Integration tests for ChatCompletion and Completions classes

Run tests with:

make format
make lint
make test

All tests passing ✅

Checklist

• Follows PR title format: fix(community): {DESCRIPTION}
• Added comprehensive unit tests (36 tests)
• Ran make format, make lint, and make test - all passing
• Changes are backward compatible
• No new dependencies added
• Only touches one package (community)
• Includes closing keyword (Fixes OpenAI message adapters missing implementation for AIMessage.tool_calls #414)