Show better error message when Model class isn't abstract

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.<init>(TableInfo.java:56)
	at org.javawebstack.orm.Repo.<init>(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

Reproduce the failure by registering a non-abstract model, then start at ORM.register and follow the stack into Repo.java and TableInfo.java, especially constructInfo, analyzeTable, and getIdType around the reported lines. Check the existing model validation and error-handling paths. Done means this misuse produces a clear exception identifying that the base model must be abstract instead of the reported NullPointerException.