Add other stream part type to createDataStream()

[yudistiraashadi]

Hello. First of all, thank you for the amazing library. This library really helps us to use multiple LLM providers easily. I'm here to suggest improvement, and perhaps if this is accepted, I can help send pull request.

Improvement Suggestion

Right now we want to add custom data to the messages sent back from our API. I saw from the docs there is createDataStreamResponse which can send back extra data to the frontend. But I don't understand why only limit it to data and annotation only? I think we can easily add more data type such as reasoning and others.

The limitation with data and annotation is it is very hard to specifically set relation between the extra data and specific message we want the data to be related to. If possible we want to e.g. add extra attachments or source programmatically via the stream.

Suggestion

What if we add more data types on the createDataStream() to accommodate other data type as listed on stream protocol