Implement hysteresis for metric status changes to prevent flapping

Add comprehensive hysteresis support to prevent status oscillation near
threshold boundaries while maintaining responsive alerting.

Key Features:
- HysteresisThresholds with configurable upper/lower limits
- StatusTracker for per-metric status history
- Default gaps: CPU load 10%, memory 5%, disk temp 5°C

Updated Components:
- CPU load collector (5-minute average with hysteresis)
- Memory usage collector (percentage-based thresholds)
- Disk temperature collector (SMART data monitoring)
- All collectors updated to support StatusTracker interface

Cache Interval Adjustments:
- Service status: 60s → 10s (faster response)
- Disk usage: 300s → 60s (more frequent checks)
- Backup status: 900s → 60s (quicker updates)
- SMART data: moved to 600s tier (10 minutes)

Architecture:
- Individual metric status calculation in collectors
- Centralized StatusTracker in MetricCollectionManager
- Status aggregation preserved in dashboard widgets

agent/src/config/loader.rs

@@ -1,18 +1,19 @@
-use anyhow::{Context, Result};
-use std::path::Path;
-use std::fs;
 use crate::config::AgentConfig;
+use anyhow::{Context, Result};
+use std::fs;
+use std::path::Path;
 
 pub fn load_config<P: AsRef<Path>>(path: P) -> Result<AgentConfig> {
     let path = path.as_ref();
     let content = fs::read_to_string(path)
         .with_context(|| format!("Failed to read config file: {}", path.display()))?;
-    
+
     let config: AgentConfig = toml::from_str(&content)
         .with_context(|| format!("Failed to parse config file: {}", path.display()))?;
-    
-    config.validate()
+
+    config
+        .validate()
         .with_context(|| format!("Invalid configuration in file: {}", path.display()))?;
-    
+
     Ok(config)
-}
+}