[Refactor] Roll out stream helpers to Friendli, Opencode Go, and MiMo specs

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What changed

• Migrated friendli.spec.ts, opencode-go.spec.ts, and mimo.spec.ts to the shared stream helpers.
• Replaced inline async-iterator and next-chain stream mocks with asyncStreamFrom, including empty done-true mocks.
• Replaced pure collect/drain loops with collectStream, keeping single-chunk .next() assertions inline where they test first-chunk behavior.
• Reduced ESLint suppressions for mimo.spec.ts and opencode-go.spec.ts after removing obsolete explicit-any declarations.

Why this change was made

This continues the approved test-utils rollout with a three-file mid-count batch, broadening the shared stream-helper idiom while preserving request-shape and first-chunk assertions.

Impact

No user-facing behavior change. One hundred eighteen targeted provider tests passed, src lint/typecheck passed, and the full Zoo-Code test suite passed after rerunning an unrelated temp-dir cleanup flake.

Related PRs

• Async-stream test-utils pilot: [Refactor] Pilot shared stream test utilities #1086
• Anthropic Vertex stream-helper migration: [Refactor] Roll out stream helpers to Anthropic Vertex spec #1094
• LiteLLM and Z.ai stream-helper batch: [Refactor] Roll out stream helpers to LiteLLM and Z.ai specs #1095

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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