fix: 统一 calc() 精度避免小米微信小程序子像素舍入差异

- diy-video-list.vue, diy-goods-list.vue: 删除重复的 3n+3 规则
  （33.33% 精度低于 33.3333333%，且与 3n 规则匹配同一组元素）
- diy-fenxiao-goods-list.vue: 两列布局统一 calc(50% - 10rpx)，
  消除第2项 1rpx 的减数差异

components-diy/diy-fenxiao-goods-list.vue

@@ -337,7 +337,7 @@ export default {
 		width: calc(50% - 10rpx);
 
 		&:nth-child(2n + 2) {
-			width: calc(50% - 11rpx);
+			width: calc(50% - 10rpx);
 			margin-right: 0;
 		}
 

components-diy/diy-goods-list.vue

@@ -1018,10 +1018,6 @@ export default {
 		width: calc(33.3333333% - 14rpx);
 		box-sizing: border-box;
 
-		&:nth-child(3n + 3) {
-			width: calc(33.33% - 15rpx);
-		}
-
 		&:nth-of-type(1),
 		&:nth-of-type(2),
 		&:nth-of-type(3) {

components-diy/diy-video-list.vue

@@ -230,10 +230,6 @@ export default {
 			width: calc(33.3333333% - 14rpx);
 			box-sizing: border-box;
 
-			&:nth-child(3n + 3) {
-				width: calc(33.33% - 15rpx);
-			}
-
 			&:nth-of-type(1),
 			&:nth-of-type(2),
 			&:nth-of-type(3) {