feat: Remove unused imports and suppress dead_code warnings across charging engine modules

- Remove unused AsyncCommands/error/ChargingSession/ErrorContext imports from credit_management
- Remove unused ErrorContext/ChargingError imports from engine
- Remove unused ErrorContext import from rating_billing and prefix unused variables with underscore
- Remove unused ErrorContext import from rating_plans_repo
- Remove unused Context import from errors/helpers
- Remove unused info/debug/SystemTime imports from monitoring
- Remove unused sleep

apps/charging-engine/src/monitoring/monitoring.rs

@@ -1,8 +1,5 @@
-use tracing::{info, debug};
-use std::time::SystemTime;
 
-use crate::errors::{ChargingError, ChargingResult, ErrorContext};
-use super::types::{SystemStats, HealthStatus};
+use crate::errors::ChargingResult;
 
 impl crate::charging::ChargingEngine {
     pub async fn get_performance_metrics(&self) -> ChargingResult<PerformanceMetrics> {

apps/charging-engine/src/monitoring/sync.rs

@@ -1,9 +1,8 @@
-use tokio::time::{interval, sleep};
+use tokio::time::interval;
 use tracing::{info, warn, error, debug};
-use std::time::Duration;
 use chrono::Datelike;
 
-use crate::errors::{ChargingError, ChargingResult, ErrorContext, log_error};
+use crate::errors::{ChargingResult, log_error};
 use crate::monitoring::types::{SystemStats, HealthStatus};
 
 impl crate::charging::ChargingEngine {

apps/charging-engine/src/monitoring/types.rs

@@ -16,6 +16,7 @@ pub struct HealthStatus {
 }
 
 #[derive(Debug, Clone)]
+#[allow(dead_code)]
 pub struct PerformanceMetrics {
     pub connected_clients: u64,
     pub used_memory: u64,
@@ -25,6 +26,7 @@ pub struct PerformanceMetrics {
 }
 
 #[derive(Debug, Clone)]
+#[allow(dead_code)]
 pub struct ErrorStats {
     pub total_errors: u64,
     pub error_types: std::collections::HashMap<String, u64>,