Update Voice

Update mutable metadata fields of a voice.

Invalidates the user_voice and user_voice_preview Redis cache entries for the affected voice after a successful update.

Args: voice_id: UUID of the voice to update. payload: Fields to update (name, description, style, etc.). token: Authenticated token with user context. _request: Raw FastAPI Request. version: API version extracted from the version request header. x_api_key: Bearer API key (used as a cache-key component for invalidation).

Returns: None: HTTP 204 No Content on success.