Structured Output Fixes

[LZL0]

Summary by cubic

Fixes retry behavior in structured() and structured_array() so stream factory functions are called fresh on each attempt and direct iterators are wrapped correctly, preventing “stream already consumed” and “ReadableStream is locked” errors.

• Bug Fixes
  • Pass factory functions directly to _internal_run; wrap direct async iterators in a lambda so buffered streams can replay across retries.
  • Apply the fix in both single-stream and multi-stream/fallback paths.
  • Add tests covering structured(), structured_array(), async factories, fallbacks, and retry/exhaustion scenarios.

^{Written for commit 7fa6674. Summary will update automatically on new commits.}

[cubic-dev-ai]

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