Generate Batch Voices 501-2000 total chars

Batch text-to-speech: synthesize up to 20 text items in a single call, standard voices only, for 501-2000 total characters, returns JSON with base64 WAV audio plus duration and sample rate per item. Use it to: batch-voice a longer set of messages, produce audio for a multi-section script or FAQ, generate several paragraph-length voice clips in one request without repeated calls. USDC on Base via x402.