- Standardize formatting by aligning and cleaning up indentation, spacing, and line breaks across multiple modules.
- Enhance logging with improved message formatting for better context and readability.
- Simplify error handling in `pkg6dev`, `pkg6repo`, and core libraries by consolidating redundant patterns and improving clarity.
- Update test cases to reflect formatting and logging changes while extending coverage of edge cases.
- Perform general cleanup, including removing unused imports, refining comments, and ensuring consistent style.
- Update `FileBackend` to store files in a multi-level directory structure (`xx/yy/hash`) based on hash prefixes.
- Adjust method signatures and logic across `FileBackend`, `pkg6dev`, and `pkg6repo` to support mutable repository operations.
- Add test cases and scripts (`test_file_structure.rs`, `test_repo_operations.sh`) to validate the new file structure.
- Refactor catalog manager to use `RefCell` for interior mutability to enable lazy initialization.
- Clean up redundant and dead code, enhance comments, and replace outdated logic for file handling and metadata operations.
