chore: update LaunchDarkly AI SDK and langchain dependencies to latest versions

[kinyoklion]

Summary

Updates LaunchDarkly AI SDK dependencies and the langchain ecosystem to their latest versions. The ldai_langchain 0.4.0 release removed the LangChainProvider class in favor of top-level helper functions, so the three langchain-based examples are updated accordingly.

Dependency changes in pyproject.toml:

Package	Old	New
launchdarkly-server-sdk-ai	^0.16.1	^0.17.0
launchdarkly-server-sdk-ai-langchain	^0.3.2	^0.4.0
launchdarkly-server-sdk-ai-openai	^0.2.1	^0.3.0
langchain	^0.3.0	^1.0.0
langchain-core	^0.3.0	^1.0.0
langchain-aws	^0.2.30	^1.0.0
langchain-openai	^0.3.30	^1.0.0
langchain-google-genai	^2.1.9	^4.0.0
langgraph	^0.2.0	^1.0.0

Code changes: LangChainProvider.get_ai_metrics_from_response → get_ai_metrics_from_response (now a top-level import from ldai_langchain) in langchain_example.py, langgraph_agent_example.py, and langgraph_multi_agent_example.py.

Review & Testing Checklist for Human

• Verify the langchain 0.x → 1.x migration doesn't break other APIs used in the examples (e.g., init_chat_model, message dict format, ainvoke). Only the LangChainProvider import was updated — other langchain usage was left as-is.
• Confirm langchain-google-genai ^4.0.0 is correct — this skips the 3.x line. Check that the gemini_example.py still works with this version.
• Verify poetry.lock is either committed or intentionally gitignored. It is not included in this diff.
• Run at least one example end-to-end (e.g., poetry run openai-example or poetry run langchain-example) to confirm the updated SDKs work with a real LaunchDarkly AI config.

Notes

• The non-langchain examples (openai_example.py, bedrock_example.py, gemini_example.py, chat_judge_example.py, chat_observability_example.py, direct_judge_example.py) were not modified. Their imports were verified to still resolve, but they were not tested end-to-end.
• The langchain ecosystem bump from 0.x to 1.x was required because ldai_langchain 0.4.0 itself depends on langchain >=1.0.0.

Link to Devin session: https://app.devin.ai/sessions/c8cf47d46e3f464290a65b6c05862c86
Requested by: @kinyoklion

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