Use max_completion_tokens for OpenAI and Azure OpenAI providers:
The OpenAI API deprecated max_tokens in favor of
max_completion_tokens for chat completions. Newer models
(gpt-4o, o1, o3) reject the old parameter with a 400 error.
AZURE_API_VERSION env var now overrides the default API version:
(falls back to 2024-12-01-preview).
Update tests to test for expected structures