feat(mapper): 添加 MpUserMapper 及用户插入测试

新增 MpUserMapper 接口，扩展自 Mybatis Plus 的 BaseMapper，用于 User 实体的数据库操作。在 UserMapperTest 中添加 testAddUser 方法以验证用户插入功能，使用 SQLite 数据库进行单元测试。

.github/workflows/maven.yml

@@ -21,6 +21,7 @@ jobs:
 
     steps:
     - uses: actions/checkout@v4
+    - run: rm -rf test.db
     - name: Set up JDK 17
       uses: actions/setup-java@v4
       with:
@@ -28,7 +29,7 @@ jobs:
         distribution: 'temurin'
         cache: maven
     - name: Build with Maven
-      run: mvn -B package -DskipTests --file pom.xml
+      run: mvn -B package --file pom.xml
 
     # Optional: Uploads the full dependency graph to GitHub to improve the quality of Dependabot alerts this repository can receive
 #    - name: Update dependency graph