refactor(mall): 优化分类查询接口参数类型和逻辑

- 将 ApiProdController 中 categoryByAncestors 方法的参数类型从 Long 改为 String
- 修改 ITzCategoryService 接口中 listByAncestors 方法的参数类型从 Long 改为 String- 更新 TzCategoryServiceImpl 中 listByAncestors 方法，移除对 subset 字段的查询条件- 优化 listByParentId 方法，移除对 subset 字段的查询条件

ruoyi-mall-api/src/main/java/org/dromara/web/controller/ApiProdController.java

@@ -225,7 +225,7 @@ public class ApiProdController {
     @GetMapping("/categoryByAncestors")
     @Operation(summary = "根据祖级ID获取分类信息列表", description = "获取所有的产品分类信息，顶级分类的ancestors为0,默认为顶级分类")
     @Parameter(name = "ancestors", description = "祖级ID")
-    public ServerResponseEntity<List<TzCategoryVo>> categoryByAncestors(@RequestParam(value = "ancestors", defaultValue = "0") Long ancestors) {
+    public ServerResponseEntity<List<TzCategoryVo>> categoryByAncestors(@RequestParam(value = "ancestors", defaultValue = "0") String ancestors) {
         List<TzCategoryVo> categories = categoryService.listByAncestors(ancestors);
         return ServerResponseEntity.success(categories);
     }