Fix: Propagate Generic Type to `GenerateStreamResponse.stream`

[Dinesh-Gautam]

Fixes: #3603

Context

The GenerateStreamResponse interface did not propagate its generic O type to the stream property.
As a result, the chunks yielded by stream were always typed as GenerateResponseChunk<unknown>,
forcing users to manually assert types and losing schema-based type inference.

What Was Changed

Updated the GenerateStreamResponse interface to propagate the generic O type to the stream property.

After Changes

Checklist (if applicable):

• [x] PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• [x] Tested (manually, unit tested, etc.)
• [ ] Docs updated (updated docs or a docs bug required)

[parkcoool]

I've encountered the same type inference issue with the stream response. It would be great if this could be merged soon as it's blocking proper TypeScript support for streaming.

[Dinesh-Gautam]

@apascal07 quick follow-up on this PR when you have a moment. Happy to adjust anything if needed. Thanks!