fix: improve error handling in searchVectorIndex method (#750)

* fix: ensure IndexReader is properly closed in searchVectorIndex method

* fix: use try-with-resources approach to avoiding exception masked

Author: SYaoJun

geaflow/geaflow-plugins/geaflow-store/geaflow-store-vector/src/main/java/org/apache/geaflow/store/lucene/GraphVectorIndex.java

@@ -136,9 +136,7 @@ public void addVectorIndex(boolean isVertex, K key, String fieldName, float[] ve
      */
     @Override
     public K searchVectorIndex(boolean isVertex, String fieldName, float[] vector, int topK) {
-        try {
-            // Open index reader
-            IndexReader reader = DirectoryReader.open(directory);
+        try (IndexReader reader = DirectoryReader.open(directory)) {
             IndexSearcher searcher = new IndexSearcher(reader);
 
             // Create KNN vector query
@@ -166,8 +164,6 @@ public K searchVectorIndex(boolean isVertex, String fieldName, float[] vector, i
                 throw new IllegalArgumentException("Unsupported key type: " + keyClass.getName());
             }
 
-            reader.close();
-
             return result;
         } catch (IOException e) {
             throw new RuntimeException("Failed to search vector index", e);