Remove all unused code and fix build warnings

- Remove unused struct fields: tier, config_name, last_collection_time
- Remove unused structs: PerformanceMetrics, PerfMonitor
- Remove unused methods: get_performance_metrics, get_collector_names, get_stats
- Remove unused utility functions and system helpers
- Remove unused config fields from CPU and Memory collectors
- Keep config fields that are actually used (DiskCollector, etc.)
- Remove unused proxy_pass_url variable and assignments
- Fix duplicate hostname variable declaration
- Achieve zero build warnings without functionality changes

agent/src/collectors/systemd.rs

@@ -6,12 +6,10 @@ use std::sync::RwLock;
 use std::time::Instant;
 use tracing::debug;
 
-use super::{Collector, CollectorError, PerformanceMetrics};
+use super::{Collector, CollectorError};
 
 /// Systemd collector for monitoring systemd services
 pub struct SystemdCollector {
-    /// Performance tracking
-    last_collection_time: Option<std::time::Duration>,
     /// Cached state with thread-safe interior mutability
     state: RwLock<ServiceCacheState>,
 }
@@ -36,7 +34,6 @@ struct ServiceCacheState {
 impl SystemdCollector {
     pub fn new() -> Self {
         Self {
-            last_collection_time: None,
             state: RwLock::new(ServiceCacheState {
                 monitored_services: Vec::new(),
                 last_discovery_time: None,
@@ -481,9 +478,6 @@ impl Collector for SystemdCollector {
         Ok(metrics)
     }
 
-    fn get_performance_metrics(&self) -> Option<PerformanceMetrics> {
-        None // Performance tracking handled by cache system
-    }
 }
 
 impl SystemdCollector {
@@ -755,7 +749,6 @@ impl SystemdCollector {
     fn parse_server_block(&self, lines: &[&str], start_index: &mut usize) -> Option<String> {
         use tracing::debug;
         let mut server_names = Vec::new();
-        let mut proxy_pass_url = None;
         let mut has_redirect = false;
         let mut i = *start_index + 1;
         let mut brace_count = 1;
@@ -785,16 +778,6 @@ impl SystemdCollector {
                 }
             }
 
-            // Extract proxy_pass URL (backend IP:port)
-            if trimmed.starts_with("proxy_pass") {
-                if let Some(url_part) = trimmed.strip_prefix("proxy_pass") {
-                    let url_clean = url_part.trim().trim_end_matches(';');
-                    if !url_clean.is_empty() {
-                        proxy_pass_url = Some(url_clean.to_string());
-                        debug!("Found proxy_pass in block: {}", url_clean);
-                    }
-                }
-            }
 
             // Check for redirects (skip redirect-only servers)
             if trimmed.contains("return") && (trimmed.contains("301") || trimmed.contains("302")) {