Vercel AI V6 class-based agents have incorrect gen_ai.operation.name mapping

V6's ToolLoopAgent with functionId set causes operation.name to be ai.streamText myAgent instead of ai.streamText. The exact-match lookup in mapVercelAiOperationName misses this, leaving gen_ai.operation.name as the raw Vercel value instead of invoke_agent. Same issue affects child generate_content and execute_tool spans. Function-based usage without functionId is unaffected.