Fix sync generator cancel ValueError (#13134)
* Fix sync generator cancel ValueError
* add changeset
* Add tests for SyncToAsyncIterator.aclose
Test the retry logic for "generator already executing"
ValueError, timeout behavior, and safe_aclose_iterator
delegation for both sync and async generators.
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Co-authored-by: gradio-pr-bot <gradio-pr-bot@users.noreply.github.com>
Co-authored-by: Freddy Boulton <41651716+freddyaboulton@users.noreply.github.com>
