Address review feedback: extract helper, fix formatting, clear removed vector

- Extract transferVector() helper to reduce duplication in addVector/removeVector
- Fix Spotless formatting violation in TestVectorSchemaRoot.java
- Clear the removed vector's buffers in removeVector() so the original root
  is consistently empty after the operation, matching the documented behaviour

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: John-W-Lewis

vector/src/main/java/org/apache/arrow/vector/VectorSchemaRoot.java

@@ -207,19 +207,12 @@ public VectorSchemaRoot addVector(int index, FieldVector vector) {
     List<FieldVector> newVectors = new ArrayList<>();
     for (int i = 0; i < fieldVectors.size(); i++) {
       if (i == index) {
-        TransferPair addPair = vector.getTransferPair(vector.getAllocator());
-        addPair.transfer();
-        newVectors.add((FieldVector) addPair.getTo());
+        newVectors.add(transferVector(vector));
       }
-      FieldVector v = fieldVectors.get(i);
-      TransferPair transferPair = v.getTransferPair(v.getAllocator());
-      transferPair.transfer();
-      newVectors.add((FieldVector) transferPair.getTo());
+      newVectors.add(transferVector(fieldVectors.get(i)));
     }
     if (index == fieldVectors.size()) {
-      TransferPair addPair = vector.getTransferPair(vector.getAllocator());
-      addPair.transfer();
-      newVectors.add((FieldVector) addPair.getTo());
+      newVectors.add(transferVector(vector));
     }
     return new VectorSchemaRoot(newVectors);
   }
@@ -240,15 +233,19 @@ public VectorSchemaRoot removeVector(int index) {
     List<FieldVector> newVectors = new ArrayList<>();
     for (int i = 0; i < fieldVectors.size(); i++) {
       if (i != index) {
-        FieldVector v = fieldVectors.get(i);
-        TransferPair transferPair = v.getTransferPair(v.getAllocator());
-        transferPair.transfer();
-        newVectors.add((FieldVector) transferPair.getTo());
+        newVectors.add(transferVector(fieldVectors.get(i)));
       }
     }
+    fieldVectors.get(index).clear();
     return new VectorSchemaRoot(newVectors);
   }
 
+  private static FieldVector transferVector(FieldVector vector) {
+    TransferPair transferPair = vector.getTransferPair(vector.getAllocator());
+    transferPair.transfer();
+    return (FieldVector) transferPair.getTo();
+  }
+
   public Schema getSchema() {
     return schema;
   }

vector/src/test/java/org/apache/arrow/vector/TestVectorSchemaRoot.java

@@ -363,8 +363,7 @@ public void testAddVectorOwnership() {
       intVector2.setValueCount(5);
       intVector3.setValueCount(5);
 
-      VectorSchemaRoot original =
-          new VectorSchemaRoot(Arrays.asList(intVector1, intVector2));
+      VectorSchemaRoot original = new VectorSchemaRoot(Arrays.asList(intVector1, intVector2));
       original.setRowCount(5);
 
       VectorSchemaRoot result = original.addVector(1, intVector3);