fix(clippy): use sort_by_key instead of sort_by for reverse sorting (#553)

- Fix cortex-apply-patch backup.rs: use sort_by_key with Reverse
- Fix cortex-compact log_pruner.rs: use sort_by_key with Reverse

These changes address clippy::unnecessary_sort_by warnings.

Author: echobt

src/cortex-apply-patch/src/backup.rs

@@ -232,7 +232,7 @@ impl BackupManager {
         }
 
         // Sort by timestamp (newest first)
-        backups.sort_by(|a, b| b.timestamp.cmp(&a.timestamp));
+        backups.sort_by_key(|b| std::cmp::Reverse(b.timestamp));
 
         Ok(backups)
     }

src/cortex-compact/src/auto_compaction/log_pruner.rs

@@ -96,7 +96,7 @@ impl LogPruner {
         }
 
         // Sort by modified time (newest first) for rotation priority
-        log_files.sort_by(|a, b| b.modified.cmp(&a.modified));
+        log_files.sort_by_key(|f| std::cmp::Reverse(f.modified));
 
         // Process each log file
         for (idx, log_file) in log_files.iter().enumerate() {