Show better error message when Model class isn't abstract

還沒有人認領這個 Issue。

**Describe the Bug**
When you extend the ORM Model to your own Model and forget to set it to abstract, you get an Exception saying
```
Exception in thread "main" java.lang.NullPointerException: Cannot invoke "java.lang.reflect.Field.getType()" because the return value of "org.javawebstack.orm.TableInfo.getField(String)" is null
at org.javawebstack.orm.TableInfo.getIdType(TableInfo.java:282)
at org.javawebstack.orm.TableInfo.analyzeTable(TableInfo.java:95)
at org.javawebstack.orm.TableInfo.constructInfo(TableInfo.java:61)
at org.javawebstack.orm.TableInfo.(TableInfo.java:56)
at org.javawebstack.orm.Repo.(Repo.java:35)
at org.javawebstack.orm.ORM.register(ORM.java:25)
at org.javawebstack.orm.ORM.register(ORM.java:37)

```
**To Reproduce**
Steps to reproduce the behavior:
1. Forget to set your model class to abstract

**Expected behavior**
Maybe show some better error message which indicates that your base model isn't abstract yet.

**Environment Information:**
- Java Language Level 21
- ORM Version 1.0.3-SNAPSHOT

透過註冊一個非抽象模型來重現失敗，然後從 ORM.register 開始追蹤堆疊，進入 Repo.java 和 TableInfo.java，尤其檢查回報行附近的 constructInfo、analyzeTable 和 getIdType。檢查現有的模型驗證與錯誤處理路徑。完成的標準是：這種誤用會產生一個清楚的例外，指出基礎模型必須是抽象的，而不是回報的 NullPointerException。

由索引模型根據 Issue 內容生成。