feat(class): 实现班级列表分页查询功能

- 新增班级后端分页接口及相关服务实现
- 实现班级与年级关联数据查询及映射
- 新增分页请求和响应VO类支持前后端数据传输
- 修改前端class.vue，增加班级列表分页展示组件
- 增加前端分页逻辑及状态管理，支持切换页码和页面大小
- 创建GradeClassDO实体及对应Mapper实现关联查询
- 优化数据库Mapper XML，增加分页查询及计数SQL语句
- 调整MyBatis配置生成grade_class表实体类和Mapper接口

enlish-service/src/main/resources/mapper/GradeClassDOMapper.xml

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
+<mapper namespace="com.yinlihupo.enlish.service.domain.mapper.GradeClassDOMapper">
+    <resultMap id="BaseResultMap" type="com.yinlihupo.enlish.service.domain.dataobject.GradeClassDO">
+        <id column="id" jdbcType="INTEGER" property="id" />
+        <result column="class_id" jdbcType="INTEGER" property="classId" />
+        <result column="grade_id" jdbcType="INTEGER" property="gradeId" />
+    </resultMap>
+    
+    <select id="selectByClassIds" resultMap="BaseResultMap">
+        select * from grade_class where class_id in
+        <foreach collection="classIds" item="classId" separator="," open="(" close=")">
+            #{classId}
+        </foreach>
+    </select>
+
+</mapper>