Add native Telnyx Speech-to-Text support using the OpenAI-compatible
REST API at https://api.telnyx.com/v2/ai/audio/transcriptions.
- Add telnyxProvider with audio transcription capability
- Reuse transcribeOpenAiCompatibleAudio since Telnyx follows OpenAI format
- Add default model: openai/whisper-large-v3-turbo
- Add tests for the new provider
Co-Authored-By: Claude (anthropic/claude-opus-4-5) <noreply@anthropic.com>
