Fix voice TTS for AI SDK textStream responses

[whoiskatrin]

Summary

Fixes withVoice handling of AI SDK streamText(...).textStream values returned from onTurn().

AI SDK textStream values are dual-protocol objects: they are ReadableStreams and also expose a custom Symbol.asyncIterator that yields string deltas. iterateText() previously checked instanceof ReadableStream first, so these streams could be consumed through the generic stream parser instead of the AI SDK string iterator. That meant assistant text could be persisted while no text reached the sentence chunker/TTS pipeline, producing no spoken audio.

This updates iterateText() to prefer a custom/source-owned async iterator before falling back to ReadableStream parsing, while preserving the existing native ReadableStream<string> and ReadableStream<Uint8Array> SSE/NDJSON paths.

Fixes #1364
Refs #1352

Changes

• Prefer custom async iterators for dual-protocol text streams in @cloudflare/voice.
• Keep native ReadableStream parsing behavior intact for string streams and SSE/NDJSON byte streams.
• Add a regression test for an AI SDK-like dual-protocol stream.
• Document that AI SDK result.textStream can be returned directly from onTurn().
• Add a patch changeset for @cloudflare/voice.

Testing

• npm test -w @cloudflare/voice
• npm run build
• npm run check

[changeset-bot]

🦋 Changeset detected

Latest commit: e06978f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@cloudflare/voice	Patch

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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commit: e06978f

[mattzcarey]

looks good and makes sense to me