[jiefenghuang]

Clear omitted Parent and ACL fields when decoding a reused Attr, while preserving KeepCache and the empty-input fallback. This prevents a parent's ACL from leaking into a child lookup.

Restore attribute preloading after #7675 by fetching each inode through the GET cache hook. Preserve open-file cache updates, skip deleted inodes, and stop on other read failures. Each uncached inode now requires one background GET.

Validation:

• Decoder, cached-lookup and preload regressions fail before the fix and pass afterward; targeted race checks pass.
• Metadata core passes with MySQL/TiKV-dependent cases excluded. Redis/SQLite/MemKV/Badger shared tests, cross-engine binary dump/load, and Redis/SQLite/Badger JSON dump/load pass.
• Non-core services are unavailable locally.