- Implement unit tests to cover `Image` creation, metadata management, saving/loading, and error handling.
- Add separate constructors for `Full` and `Partial` image types (`new_full`, `new_partial`).
- Introduce robust path handling methods (`metadata_dir`, `image_json_path`) for consistent metadata structure.
- Enhance error diagnostics with `InvalidPath` variant in `ImageError`.
- Update `Cargo.toml` for test module inclusion.
- Introduce `#[serde(skip_serializing_if = "is_empty", default)]` for various optional fields to streamline serialization and ensure defaults are applied during deserialization.
- Add `tracing::debug` logging for enhanced error context in JSON deserialization fallback logic.
- Update tests to reflect changes in manifest parsing, including new cases for the updated JSON format.
