feat: Consistently include original in "Unexpected response" errors

[mweidner037]

We're encountering these while using ChatGoogleAI but with original: nil. The PR adds original in that case, as well as in the other Chat... classes at an analogous place.

Note: There is a difference in the error messages returned in the "Unexpected response" case for streaming vs non-streaming, consistently across chat models. If you like, I can make them consistent with each other, in either direction.

# do_api_request(...{stream: false}...):
      other ->
        Logger.error("Unexpected and unhandled API response! #{inspect(other)}")
        other

# do_api_request(...{stream: true}...):
      other ->
        Logger.error(
          "Unhandled and unexpected response from streamed post call. #{inspect(other)}"
        )

        {:error,
         LangChainError.exception(
           type: "unexpected_response",
           message: "Unexpected response",
           original: other
         )}