Langchain + Azure OpenAI proxy getting resource not found error
## Context
Routing LangChain's AzureChatOpenAI through the Helicone proxy fails with `Resource not found` from OpenAI. Calling OpenAI directly through the same proxy URL works fine.
## Verified resolution
Maintainer chitalian: with the LangChain Azure wrapper, drop the `v1` from the Helicone proxy base URL, i.e. use `https://oai.hconeai.com` (not `https://oai.hconeai.com/v1`) as `openai_api_base`. The maintainer added this to the docs in PR #971.