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 el fallo registrando un modelo no abstracto y empieza en ORM.register para seguir el stack hasta Repo.java y TableInfo.java, especialmente por constructInfo, analyzeTable y getIdType alrededor de las líneas indicadas. Comprueba las rutas existentes de validación de modelos y manejo de errores. Se considera terminado cuando este uso incorrecto produce una excepción clara que identifique que el modelo base debe ser abstracto, en lugar de la NullPointerException indicada.