When using Azure AI Foundry Cohere rerank endpoints, the Cohere SDK
incorrectly appends /v1/rerank to the base_url, but Azure endpoints
already include the full path (e.g., /models/.../invoke). This causes
double-pathing and 404 errors.
This commit modifies CohereCrossEncoder to detect when base_url is
provided and use httpx directly for custom endpoints, while keeping
the native Cohere SDK for standard API usage. The Azure Cohere API
response format is compatible with the native format.
Fixes#783
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
