feat: Remove api module and relocate handlers, clean up unused code and dead_code attributes

- Delete api.rs module containing 20+ handler functions (credit management, subscriber accounts, rating plans, user blocking, system stats, metrics, engine control, error stats, sync control, health checks)
- Remove dead_code attributes from UsageEvent and UsageType in charging/types
- Remove validate_imsi helper function and dead_code attribute from errors/helpers
- Remove ConfigurationError logging case

apps/charging-engine/src/errors/helpers.rs

@@ -68,23 +68,6 @@ pub fn validate_bytes(bytes: u64) -> ChargingResult<()> {
     Ok(())
 }
 
-#[allow(dead_code)]
-pub fn validate_imsi(imsi: &str) -> ChargingResult<()> {
-    if imsi.is_empty() {
-        return Err(ChargingError::InvalidInput("IMSI cannot be empty".to_string()));
-    }
-
-    if imsi.len() < 15 || imsi.len() > 15 {
-        return Err(ChargingError::InvalidInput("IMSI must be exactly 15 digits".to_string()));
-    }
-
-    if !imsi.chars().all(|c| c.is_ascii_digit()) {
-        return Err(ChargingError::InvalidInput("IMSI must contain only digits".to_string()));
-    }
-
-    Ok(())
-}
-
 pub fn validate_session_id(session_id: &str) -> ChargingResult<()> {
     if session_id.is_empty() {
         return Err(ChargingError::InvalidInput("Session ID cannot be empty".to_string()));
@@ -161,9 +144,6 @@ pub fn log_error(error: &ChargingError) {
         ChargingError::SerializationError(msg) => {
             tracing::error!("Serialization error: {}", msg);
         }
-        ChargingError::ConfigurationError(msg) => {
-            tracing::error!("Configuration error: {}", msg);
-        }
         ChargingError::InternalError(msg) => {
             tracing::error!("Internal error: {}", msg);
         }

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

@@ -13,8 +13,6 @@ pub enum ChargingError {
     UsageBlocked(String),
     InvalidInput(String),
     SerializationError(String),
-    #[allow(dead_code)]
-    ConfigurationError(String),
     InternalError(String),
 }
 
@@ -31,7 +29,6 @@ impl fmt::Display for ChargingError {
             ChargingError::UsageBlocked(reason) => write!(f, "Usage blocked: {}", reason),
             ChargingError::InvalidInput(msg) => write!(f, "Invalid input: {}", msg),
             ChargingError::SerializationError(msg) => write!(f, "Serialization error: {}", msg),
-            ChargingError::ConfigurationError(msg) => write!(f, "Configuration error: {}", msg),
             ChargingError::InternalError(msg) => write!(f, "Internal error: {}", msg),
         }
     }
@@ -52,7 +49,6 @@ impl IntoResponse for ChargingError {
             ChargingError::UsageBlocked(reason) => (StatusCode::FORBIDDEN, reason),
             ChargingError::InvalidInput(msg) => (StatusCode::BAD_REQUEST, msg),
             ChargingError::SerializationError(msg) => (StatusCode::INTERNAL_SERVER_ERROR, msg),
-            ChargingError::ConfigurationError(msg) => (StatusCode::INTERNAL_SERVER_ERROR, msg),
             ChargingError::InternalError(msg) => (StatusCode::INTERNAL_SERVER_ERROR, msg),
         };