feat: add voice data URL management and remote model settings

[TawanaState]

No description provided.

[TawanaState]

This PR introduces new features to improve flexibility in model and voice data management:

Voice Data URL Management: Added setVoiceDataUrl() in voices.js to allow dynamic configuration of the voice data source URL.
Exposed a setter voiceDataUrl on the env object for runtime updates.

Remote/Local Model Settings: Added getters and setters for allowRemoteModels, allowLocalModels, and localModelPath on the env object. These allow runtime control over model loading behavior and local model path configuration.

Motivation
These changes make it easier to:

• Switch between different voice data sources without code changes.
• Control model loading (remote/local) and paths at runtime, supporting more flexible deployment and testing scenarios.

Request
Please review and consider merging this into the main branch.
Let me know if you have any feedback or require further changes.

[canadaduane]

It looks like this or an equivalent commit was merged in: d7654ba

Update: But unfortunately setVoiceDataUrl is not made available outside the kokoro.js package, so I guess it can't be used.