chore: prefer named exports (#8315)

* chore: prefer named exports

* chore: fix import

src/picker/Picker.tsx

@@ -14,7 +14,7 @@ import { useChildren } from '@vant/use';
 import { useExpose } from '../composables/use-expose';
 
 // Components
-import Loading from '../loading';
+import { Loading } from '../loading';
 import Column, {
   PICKER_KEY,
   PickerColumn,

src/picker/demo/index.vue

@@ -77,7 +77,7 @@
 import { ref, computed, reactive, toRefs } from 'vue';
 import { dateColumns, cascadeColumns, cascadeColumnsCustomKey } from './data';
 import { useTranslate } from '@demo/use-translate';
-import Toast from '../../toast';
+import { Toast } from '../../toast';
 
 const i18n = {
   'zh-CN': {

src/picker/test/cascade.legacy.js

@@ -1,4 +1,4 @@
-import Picker from '..';
+import { Picker } from '..';
 import { mount, triggerDrag } from '../../../test';
 
 const COLUMNS = [

src/picker/test/index.spec.tsx

@@ -1,6 +1,6 @@
-import Picker from '..';
-import PickerColumn from '../PickerColumn';
 import { later, mount, triggerDrag } from '../../../test';
+import { Picker } from '..';
+import PickerColumn from '../PickerColumn';
 
 const simpleColumn = ['1990', '1991', '1992', '1993', '1994', '1995'];
 const columns = [