Bug: Entity constructor suppliers not registered in default SimpleEntityMetaFactory

[philipgreat]

Bug: Entity constructor suppliers not registered in default SimpleEntityMetaFactory

Description

When executing database queries (e.g. Q.outboxEvents()...executeForList(ctx)), the mapped rows are converted to Java entity instances. The mapping repository calls descriptor.createEntity(), which relies on entitySupplier to instantiate the classes:

public Entity createEntity() {
    if (entitySupplier == null) {
        throw new IllegalStateException("No entity supplier registered for " + getType());
    }
    return entitySupplier.get();
}

The default SimpleEntityMetaFactory resolved by the registry contains metadata configurations but does not associate or register these constructor suppliers. As a result, query execution throws:
java.lang.IllegalStateException: No entity supplier registered for OutboxEvent

Expected Behavior

Entity descriptors should automatically resolve their class constructors using reflection or have registrations automatically generated without requiring users to register constructor suppliers manually on boot.

Suggested Solution

1. Generator-side registration: Update the code generator to emit constructor supplier registration statements inside the generated EntityMetaRegistry.java file (e.g., entityDescriptor.setEntitySupplier(OutboxEvent::new)).
2. Reflection-based Fallback: Update EntityDescriptor or SimpleEntityMetaFactory to automatically construct a default constructor supplier using reflection if entitySupplier is null:

   if (entitySupplier == null && targetType != null) {
       entitySupplier = () -> {
           try {
               return targetType.getDeclaredConstructor().newInstance();
           } catch (Exception e) {
               throw new RuntimeException("Failed to instantiate " + targetType, e);
           }
       };
   }