refactor: simplify UInt64 conversion in extractRowAddresses

Use UInt8Vector.getObjectNoOverflow().longValue() directly with a
comment noting it follows the same pattern as UInt8Accessor.getLong().
Removed unnecessary BigInteger cast.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: beinan

lance-spark-base_2.12/src/main/java/org/lance/spark/internal/LanceFragmentColumnarBatchScanner.java

@@ -105,11 +105,11 @@ private long[] extractRowAddresses(
     FieldVector lastVector = rootVectors.get(rootVectors.size() - 1);
     if (LanceConstant.ROW_ADDRESS.equals(lastVector.getField().getName())
         && lastVector instanceof UInt8Vector) {
+      // UInt64 → long conversion follows the same pattern as UInt8Accessor.getLong()
       UInt8Vector rowAddrVector = (UInt8Vector) lastVector;
       long[] rowAddresses = new long[rowCount];
       for (int i = 0; i < rowCount; i++) {
-        rowAddresses[i] =
-            ((java.math.BigInteger) rowAddrVector.getObjectNoOverflow(i)).longValue();
+        rowAddresses[i] = rowAddrVector.getObjectNoOverflow(i).longValue();
       }
       return rowAddresses;
     }