Makes a streaming POST request to Anthropic and processes their SSE format.
Anthropic uses event types like content_block_delta instead of OpenAI's format.
Also handles OpenAI-compatible format for proxy servers.
stream_anthropic(url, headers, body, callback)A GenerateResult object.
The API endpoint URL.
A named list of HTTP headers.
The request body (will be converted to JSON).
A function called for each text delta.