refactor: apply rust best practices and fix memory optimizations

- Optimized memory allocation in router.rs by offloading JSON serialization to spawn_blocking and using references.
- Prevented full graph duplication on startup in state.rs index rebuild.
- Eliminated massive String allocations in QueryGraphPathHandler BFS loops.
- Avoided temporary Strings in VisualizeGraphHandler via inline writing.
- Fixed O(N) full-graph deduplication in MergeEntitiesHandler to scale efficiently.

server/src/api/rest.rs

@@ -113,8 +113,8 @@ mod tests {
     use super::*;
     use crate::router::MemoryHandler;
     use crate::state::MemoryState;
-    use std::sync::atomic::AtomicUsize;
     use std::sync::RwLock;
+    use std::sync::atomic::AtomicUsize;
     use tempfile::tempdir;
 
     #[tokio::test]
@@ -137,7 +137,9 @@ mod tests {
             block: None,
             reason: None,
         };
-        let res_set = gate_set_handler(State(app_state.clone()), Json(set_req)).await.unwrap();
+        let res_set = gate_set_handler(State(app_state.clone()), Json(set_req))
+            .await
+            .unwrap();
         assert_eq!(res_set.into_response().status(), axum::http::StatusCode::OK);
 
         // Verify the gate (and consume it)
@@ -148,8 +150,13 @@ mod tests {
             params: HashMap::new(),
             consume: true,
         };
-        let res_verify = gate_verify_handler(State(app_state.clone()), Query(verify_req)).await.unwrap();
-        assert_eq!(res_verify.into_response().status(), axum::http::StatusCode::OK);
+        let res_verify = gate_verify_handler(State(app_state.clone()), Query(verify_req))
+            .await
+            .unwrap();
+        assert_eq!(
+            res_verify.into_response().status(),
+            axum::http::StatusCode::OK
+        );
 
         // Verify again should fail since it was consumed
         let verify_req2 = GateVerifyReq {

server/src/api/setup.rs

@@ -201,16 +201,16 @@ pub fn create_router(app_state: Arc<AppState>) -> Router {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::AppState;
     use crate::router::MemoryHandler;
     use crate::state::MemoryState;
-    use crate::AppState;
-    use axum::http::Request;
     use axum::body::Body;
-    use std::sync::atomic::AtomicUsize;
-    use std::sync::RwLock;
+    use axum::http::Request;
     use std::collections::HashMap;
-    use tower::ServiceExt;
+    use std::sync::RwLock;
+    use std::sync::atomic::AtomicUsize;
     use tempfile::tempdir;
+    use tower::ServiceExt;
 
     #[tokio::test]
     async fn test_create_router_health() {
@@ -221,15 +221,15 @@ mod tests {
             clients: RwLock::new(HashMap::new()),
             next_id: AtomicUsize::new(1),
         });
-        
+
         let app = create_router(app_state);
-        
+
         // Test health endpoint
         let request = Request::builder()
             .uri("/health")
             .body(Body::empty())
             .unwrap();
-            
+
         let response = app.oneshot(request).await.unwrap();
         assert_eq!(response.status(), 200);
     }

server/src/api/ws.rs

@@ -146,10 +146,10 @@ pub async fn handle_socket(socket: WebSocket, state: Arc<AppState>, _client_type
 #[cfg(test)]
 mod tests {
     use super::*;
-    use std::sync::atomic::AtomicUsize;
-    use std::sync::RwLock;
     use crate::router::MemoryHandler;
     use crate::state::MemoryState;
+    use std::sync::RwLock;
+    use std::sync::atomic::AtomicUsize;
     use tempfile::tempdir;
 
     #[tokio::test]
@@ -163,7 +163,11 @@ mod tests {
         });
 
         // Insert a dummy client
-        app_state.clients.write().unwrap().insert("test-session".to_string(), tokio::sync::mpsc::channel(1).0);
+        app_state
+            .clients
+            .write()
+            .unwrap()
+            .insert("test-session".to_string(), tokio::sync::mpsc::channel(1).0);
 
         let send_task = tokio::spawn(async {});
         let recv_task = tokio::spawn(async {});