refactor: Transition to new modular charging and error handling architecture

- Alias charging_new as charging and errors_new as errors
- Add new charging module imports (charging_types, charging_engine, credit_management, rating_billing, monitoring_sync, sync_operations, monitoring)
- Add new error module imports (error_types, error_helpers)
- Prepare for gradual migration from monolithic to modular structure

apps/charging-engine/src/main.rs

@@ -1,8 +1,19 @@
 mod api;
-mod charging;
+mod charging_new as charging;
-mod errors;
+mod errors_new as errors;
 mod models;
 
+// Include the new modular components
+mod charging_types;
+mod charging_engine;
+mod credit_management;
+mod rating_billing;
+mod monitoring_sync;
+mod sync_operations;
+mod monitoring;
+mod error_types;
+mod error_helpers;
+
 use anyhow::Result;
 use std::sync::Arc;
 use tracing::info;