- Introduce `NULL_HASH` constant to indicate the absence of original manifest storage.
- Add `new_with_null_hash` method to create metadata for obsoleted packages without storing full manifests.
- Implement on-the-fly generation of minimal manifests with obsoletion attributes for packages with null hash.
- Update `pkg5_import` to use null hash for obsoleted packages, reducing storage requirements.
- Document null hash usage and its benefits in `obsoleted_packages.md`.
- Add `obsoleted.rs` module to handle storing, metadata management, and operations for obsoleted packages.
- Implement commands for marking, listing, searching, restoring, exporting, and importing obsoleted packages (`pkg6repo`).
- Enhance `RepositoryError` with `From` implementations for various error types to manage database and serialization-related errors.
- Introduce reusable data structures for obsoleted package metadata and export representation.
- Update `Cargo.toml` and `Cargo.lock` to include new dependencies (`redb`, `bincode`, etc.).
- Document obsoleted package workflow and integration details in `doc/obsoleted_packages.md` for contributors.
- Refactor repository internals to integrate obsoleted package support without disrupting existing workflow.
- Add robust error handling, logging, and pagination for enhanced usability and scalability.
