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/scrub_scheduler.rs

@@ -5,7 +5,6 @@
 
 use std::sync::Arc;
 use std::path::PathBuf;
-use std::time::Duration;
 
 use super::{VfsBackend, VfsError};
 use super::checksum::{scrub_all, ScrubResult};
@@ -180,7 +179,7 @@ impl ScrubStats {
 }
 
 fn format_timestamp(secs: u64) -> String {
-    use chrono::{DateTime, Utc, TimeZone};
+    use chrono::{Utc, TimeZone};
     Utc.timestamp_opt(secs as i64, 0)
         .single()
         .map(|dt| dt.format("%Y-%m-%d %H:%M:%S UTC").to_string())