UnwrapExtension

Unwrap a single in-process projection value to its observable payload type:

• Promise<T> / PromiseLike<T> → T (final-value transformers)
• StreamChannel<T> / AsyncIterable<T> → T (streaming transformers)
• anything else → the value itself

This lets a ThreadStream<TExtensions> generic accept the same shape that graph.streamEvents(..., { version: "v3" }) returns in-process (via InferExtensions<TTransformers> from @langchain/langgraph), without forcing users to redeclare payload types on the remote side.