优化 Arith.round() 方法，去除不必要的中间变量

ruoyi-common/src/main/java/com/ruoyi/common/utils/Arith.java

@@ -108,7 +108,6 @@ public class Arith
                     "The scale must be a positive integer or zero");
         }
         BigDecimal b = new BigDecimal(Double.toString(v));
-        BigDecimal one = BigDecimal.ONE;
-        return b.divide(one, scale, RoundingMode.HALF_UP).doubleValue();
+        return b.divide(BigDecimal.ONE, scale, RoundingMode.HALF_UP).doubleValue();
     }
 }