Function create_function_execution_streaming 

pub async fn create_function_execution_streaming<H: McpHandler>(
    client: &HttpClient,
    params: FunctionExecutionCreateParams,
    handler: H,
) -> Result<(impl Stream<Item = Result<FunctionExecutionChunk, HttpError>> + Send + Unpin + 'static + use<H>, Notifier), HttpError>

Creates a streaming function execution. Returns (Stream<Chunk>, Notifier); see [crate::agent::completions::http::create_agent_completion_streaming] for the demux + handler semantics.