This PR adds an aclose method to the LangGraphClient.
When using the client in a FastAPI application, it's common to share a
single instance across the application's lifespan. The absence of an
aclose method makes it difficult to gracefully close the underlying HTTP
session on application shutdown. This change enables proper resource
management by allowing the client to be closed cleanly.
Added a js-example to show it builds
Adapted integration tests after removing the test CLI command
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Co-authored-by: Nuno Campos <nuno@langchain.dev>
