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/handlers/workspaces.rs

@@ -368,14 +368,14 @@ use crate::handlers::utils::*;
 #[cfg(test)]
 mod tests {
     use super::*;
-    use tempfile::tempdir;
     use serde_json::json;
+    use tempfile::tempdir;
 
     #[tokio::test]
     async fn test_workspace_lifecycle() {
         let dir = tempdir().unwrap();
         let state = Arc::new(MemoryState::new(dir.path().to_str().unwrap()));
-        
+
         let save_handler = SaveContextWorkspaceHandler;
         let args = json!({
             "name": "wsl-session",
@@ -383,12 +383,15 @@ mod tests {
             "pinned_files": ["src/main.rs"],
             "active_task_ids": ["123"]
         });
-        
+
         let res = save_handler.execute(args, state.clone()).await.unwrap();
         assert_eq!(res, "Context workspace saved");
 
         let list_handler = ListContextWorkspacesHandler;
-        let res2 = list_handler.execute(json!({"namespace": "global"}), state.clone()).await.unwrap();
+        let res2 = list_handler
+            .execute(json!({"namespace": "global"}), state.clone())
+            .await
+            .unwrap();
         assert!(res2.contains("wsl-session"));
         assert!(res2.contains("src/main.rs"));
     }
@@ -397,7 +400,7 @@ mod tests {
     async fn test_snippets_and_pr_checklists() {
         let dir = tempdir().unwrap();
         let state = Arc::new(MemoryState::new(dir.path().to_str().unwrap()));
-        
+
         let store_handler = StoreSnippetHandler;
         let args_snip = json!({
             "name": "init_db",
@@ -406,11 +409,20 @@ mod tests {
             "code": "SELECT 1;",
             "namespace": "global"
         });
-        let res1 = store_handler.execute(args_snip, state.clone()).await.unwrap();
+        let res1 = store_handler
+            .execute(args_snip, state.clone())
+            .await
+            .unwrap();
         assert_eq!(res1, "Snippet 'init_db' stored.");
 
         let search_handler = SearchSnippetsHandler;
-        let _res2 = search_handler.execute(json!({"query": "SELECT", "namespace": "global"}), state.clone()).await.unwrap();
+        let _res2 = search_handler
+            .execute(
+                json!({"query": "SELECT", "namespace": "global"}),
+                state.clone(),
+            )
+            .await
+            .unwrap();
         // Skip assertion since it requires index rebuild
 
         let pr_handler = AddPrChecklistItemHandler;
@@ -422,25 +434,46 @@ mod tests {
         assert_eq!(res3, "PR checklist item added");
 
         let get_pr = GetPrChecklistHandler;
-        let res4 = get_pr.execute(json!({"namespace": "global"}), state.clone()).await.unwrap();
+        let res4 = get_pr
+            .execute(json!({"namespace": "global"}), state.clone())
+            .await
+            .unwrap();
         assert!(res4.contains("Check coverage"));
 
         // Pin lifecycle
         let pin = PinFileHandler;
-        let res5 = pin.execute(json!({"file_path": "src/lib.rs", "namespace": "global"}), state.clone()).await.unwrap();
+        let res5 = pin
+            .execute(
+                json!({"file_path": "src/lib.rs", "namespace": "global"}),
+                state.clone(),
+            )
+            .await
+            .unwrap();
         assert_eq!(res5, "File pinned");
-        
+
         let list_pins = ListPinnedFilesHandler;
-        let res6 = list_pins.execute(json!({"namespace": "global"}), state.clone()).await.unwrap();
+        let res6 = list_pins
+            .execute(json!({"namespace": "global"}), state.clone())
+            .await
+            .unwrap();
         assert!(res6.contains("src/lib.rs"));
 
         let unpin = UnpinFileHandler;
-        let res7 = unpin.execute(json!({"file_path": "src/lib.rs", "namespace": "global"}), state.clone()).await.unwrap();
+        let res7 = unpin
+            .execute(
+                json!({"file_path": "src/lib.rs", "namespace": "global"}),
+                state.clone(),
+            )
+            .await
+            .unwrap();
         assert_eq!(res7, "File unpinned");
 
         // Clear PR
         let clear_pr = ClearPrChecklistHandler;
-        let res8 = clear_pr.execute(json!({"namespace": "global"}), state.clone()).await.unwrap();
+        let res8 = clear_pr
+            .execute(json!({"namespace": "global"}), state.clone())
+            .await
+            .unwrap();
         assert_eq!(res8, "PR checklist cleared");
     }
 }