feat(openai): Include support for reasoning blocks when using openai compatible llm gateways

[flemx]

Description:

Include reasoning and thinking blocks inside additional_args for AIMessage when using reasoning models with custom llm gateway proxies.

This makes the openai chatmodel compatible with OpenAI compatible LLM Gateways such as the LiteLLM proxy with reasoning and thinking models like anthropic and deepseek:
https://docs.litellm.ai/docs/reasoning_content

Issue:
Fixes #30530

Dependencies:

• needs httpx in test dependencies of the openai partner library in order to ignore the self signed certs when using custom proxies for the integration test

Lint and test

• make format — passed
• make lint — passed
• make test — passed
• make integration_tests — passed

[codspeed-hq]

CodSpeed Performance Report

Merging #34049 will not alter performance

_{Comparing flemx:flemx/openai-reasoning-blocks (66223c5) with master (525d5c0)¹}

Summary

✅ 6 untouched
⏩ 28 skipped²

Footnotes

1. No successful run was found on master (ee3373a) during the generation of this report, so 525d5c0 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

2. 28 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[flemx]

TODO:

• Also need to include them inside the streaming chunks