Merge pull request #423 from Aliothmoon/feat/geni

feat: 为Spring的ServiceImpl#getMapper返回具体的约束泛型类型

mybatis-flex-spring/src/main/java/com/mybatisflex/spring/service/impl/ServiceImpl.java

@@ -34,7 +34,7 @@ public class ServiceImpl<M extends BaseMapper<T>, T> implements IService<T> {
     protected M mapper;
 
     @Override
-    public BaseMapper<T> getMapper() {
+    public M getMapper() {
         return mapper;
     }