[+] add sqlite cache and archive sync for archlinux package
1. add cache_db.py: sqlite3 ORM with pydantic row models, typed streaming;
2. add archive.py: archive sync logic, list-dates, list-packages, show-versions cli;
3. cache_db stores snapshots, packages, relations, local_packages, signatures;
4. archive.py delegates cli subparser to archive.main(), keeps cli.py thin;
5. sync downloads .db files per date, parses into sqlite, skips unchanged;
6. supports date ranges with configurable step;
LLM
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