Apply clippy fixes for code quality

Clippy Fixes Applied:
- Removed unused imports
- Fixed manual implementation of .is_multiple_of()
- Fixed unnecessary_sort_by suggestions
- Added missing Ipv4Addr imports

Files Modified:
- forward_acl.rs: Add Ipv4Addr import
- known_hosts.rs: Add Ipv4Addr import
- Various files: Remove unused imports

Build: ✅ markbase-core
Tests: 495 passed

markbase-core/src/vfs/backup_manifest.rs

@@ -3,10 +3,9 @@
 //! Compatible with ZFS send/receive and Proxmox Backup Server format
 
 use std::path::PathBuf;
-use std::time::SystemTime;
 
 use serde::{Serialize, Deserialize};
-use sha2::{Sha256, Digest};
+use sha2::Digest;
 
 use super::{VfsCompression};
 use super::checksum::VfsChecksumFile;