Refactor metadata sync service to use a prioritized provider fallback system when handling deleted CivitAI models. The new approach:
1. Attempts civarchive_api provider first for deleted models
2. Falls back to sqlite provider if archive DB is enabled
3. Maintains existing default provider behavior for non-deleted models
4. Tracks provider attempts and errors for better debugging
This improves reliability when fetching metadata for deleted models by trying multiple sources before giving up, and provides clearer error messages based on which providers were attempted.
- Introduced a new CheckpointMetadata dataclass to encapsulate metadata for checkpoint models.
- Included fields for file details, model specifications, and additional attributes such as resolution and architecture.
- Implemented a __post_init__ method to initialize tags as an empty list if not provided, ensuring consistent data handling.
