test(node): Cover LangChain model calls made from a tool without config

[RulaKhaled]

@langchain/core@1.2.17 changed which keys of the ambient runnable config reach runs started without a config (langchain-ai/langchainjs#11849). Our conversation id and span parenting for those runs depend on that ambient config, so this adds a test where a streamed runnable calls a tool, and the tool invokes a chain and model with no config.

Nothing regressed. The spans are identical on 1.2.16 and 1.2.17, since the release only adds context to the keys it passes down. The scenario initializes LangChain's AsyncLocalStorage the way LangGraph does on import. Plain @langchain/core keeps a no-op store, so no ambient config would reach the tool without it.

Closes #25293

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