[Refactor] Roll out stream helpers to OpenAI spec

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Created by Roomote. Follow up by mentioning @roomote, in the web UI, or in Discord.

What changed

• Migrated the standalone openai.spec.ts follow-up to the shared stream helpers.
• Replaced every inline Symbol.asyncIterator mock, including both async function* generators and custom next-chain iterators, with asyncStreamFrom.
• Replaced all pure collect loops and empty drain loops with collectStream, including rejection-drain loops inside expect(...).rejects.
• Reduced the openai.spec.ts ESLint suppressions count from 25 to 4 after removing obsolete chunks: any[] declarations.

Why this change was made

This is the deferred larger follow-up from the previous batch, kept as its own PR so the diff stays reviewable while still clearing one of the biggest remaining provider-spec stream-mock files.

Impact

No user-facing behavior change. One of the largest provider specs now uses the shared stream-helper idiom, the full spec passed, src lint/typecheck passed, and the full Zoo-Code test suite passed.

Related PRs

• Async-stream test-utils pilot: [Refactor] Pilot shared stream test utilities #1086
• OpenAI-family stream-helper batch: [Refactor] Batch roll out stream helpers to OpenAI-family specs #1091
• Base OpenAI stream-helper batch: [Refactor] Roll out stream helpers to base OpenAI specs #1092

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No code issues found. See task

Reviewed the stream-helper rollout in openai.spec.ts: every replaced inline Symbol.asyncIterator mock and collect/drain loop maps cleanly onto asyncStreamFrom/collectStream, all 64 spec tests pass locally, ESLint passes with the reduced suppression count of 4 (matching the actual remaining any usages), and there is no user-facing behavior change.

_{Reviewed 8890636}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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