fix: time out non-SSE streams

[Davide95]

Issue for this PR

Fixes#31122

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Makes the existing opt-in chunkTimeout wrap every streamed response body rather than only text/event-stream responses. This detects stalled EventStream and other non-SSE provider streams without reintroducing the global timeout that caused false positives for slow models.

How did you verify your code works?

• Added tests to cover it
• Tested locally, and the issue seems gone
• 4 people tried it for ~24 hours, and they confirmed the bug is fixed

Screenshots / recordings

N/A

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍

[rock-solid-sites]

Controlled reproduction added to issue #26487 confirms the proposed approach; it also covers the application/json case — a non-SSE response bypasses chunkTimeout entirely and hangs with zero errors. See the table in the #26487 comment.