[Refactor] Pilot shared stream test utilities

[zoomote]

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

What changed

• Added src/test-utils/stream.ts with typed asyncStreamFrom and collectStream helpers for async iterable setup and stream collection in tests.
• Refactored src/api/providers/__tests__/openai-native.spec.ts to use those helpers for repeated SDK stream mocks and collect-then-assert loops.
• Updated the ESLint suppressions ledger for the removed explicit-any violation in that spec.

Why this change was made

This is a small pilot for the approved test-utils plan: reduce mechanical duplication in tests without hiding scenario intent or changing production behavior.

Impact

No user-facing behavior change. The pilot gives agents a reusable async-stream test pattern, keeps assertions explicit, and passed the targeted spec, full Zoo-Code test suite, typecheck, and lint.

[zoomote]

No code issues found. See task

_{Reviewed 6dce4d0}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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