fix(bigquery): resultSet.getLong() does not truncate for large int64 values (googleapis#13718)

Fixes
[googleapis#12938](googleapis#12938)

This fixes `BigQueryResultImpl.ResultSet#getLong(int)` for Read API
rows. The index-based getter previously delegated to `getInt(String)`,
which truncated large INT64 values and could return negative results.

A regression test now verifies that `getLong(int)` preserves a value
larger than `Integer.MAX_VALUE`.

Tests:
- `mvn -pl java-bigquery/google-cloud-bigquery
-Dtest=BigQueryResultImplTest -DskipITs=true test`

Author: mahitha-ada

java-bigquery/google-cloud-bigquery/src/main/java/com/google/cloud/bigquery/BigQueryResultImpl.java

@@ -475,7 +475,7 @@ public long getLong(int columnIndex) throws SQLException {
         wasNull = false;
         return fieldValue.getNumericValue().longValue();
       } else { // Data received from Read API (Arrow)
-        return getInt(schemaFieldList.get(columnIndex).getName());
+        return getLong(schemaFieldList.get(columnIndex).getName());
       }
     }
 

java-bigquery/google-cloud-bigquery/src/test/java/com/google/cloud/bigquery/BigQueryResultImplTest.java

@@ -293,4 +293,27 @@ void testResultSetReadApi() throws InterruptedException, SQLException {
 
     assertThat(resultSet.next()).isFalse();
   }
+
+  @Test
+  void testResultSetReadApiGetLongByColumnIndexPreservesInt64Value()
+      throws InterruptedException, SQLException {
+    long largeInt64Value = 3_000_000_000L;
+    BlockingQueue<BigQueryResultImpl.Row> buffer = new LinkedBlockingDeque<>(BUFFER_SIZE);
+
+    Map<String, Object> rowValues = new HashMap<>();
+    rowValues.put("long", largeInt64Value);
+    buffer.put(new BigQueryResultImpl.Row(rowValues));
+    buffer.put(new BigQueryResultImpl.Row(null, true)); // End of buffer marker.
+
+    BigQueryResultImpl<BigQueryResultImpl.Row> bigQueryResult =
+        new BigQueryResultImpl<>(SCHEMA, 1, buffer, null);
+    ResultSet resultSet = bigQueryResult.getResultSet();
+
+    assertThat(resultSet.next()).isTrue();
+    assertThat(resultSet.getLong(1)).isEqualTo(largeInt64Value);
+    assertThat(resultSet.wasNull()).isFalse();
+    assertThat(resultSet.getLong("long")).isEqualTo(largeInt64Value);
+    assertThat(resultSet.wasNull()).isFalse();
+    assertThat(resultSet.next()).isFalse();
+  }
 }