Verify LangChain conversation id and span parenting with @langchain/core 1.2.17 #25293

`@langchain/core@1.2.17` changed how runtime context flows through the ambient runnable config across tool calls, nested runnables, and streaming (langchain-ai/langchainjs#11849).

We read the conversation id from `config.configurable` in `getConversationIdMetadataFromConfig` (`packages/server-utils/src/ai/langchain/utils.ts`), and the 1.1.40 change already forced a workaround there. This release could break that path again, or start surfacing the id twice.

Add an integration test that invokes a nested runnable from inside a streamed tool callback, and check that span parenting, `gen_ai.conversation.id`, and tags hold at every boundary on both 1.2.16 and 1.2.17.