Avram::NeedyInitializer#inherit_needs error message is less than helpful.

This error message is less than helpful. The real error is "that class should be abstract".
```
crystal spec
Showing last frame. Use --error-trace for full trace.

There was a problem expanding macro 'inherit_needs'

Code in macro 'inherited'

Called macro defined in lib/avram/src/avram/needy_initializer_and_delete_methods.cr:15:3

15 | macro inherit_needs

Which expanded to:

> 4 |
> 5 | {% if !@type.ancestors.first.abstract? %}
> 6 | {% for type_declaration in @type.ancestors.first.constant :OPERATION_NEEDS %}
^-------
Error: BUG: DeleteHierarchical(Forum) has no types
```

Start by reproducing the failure with `crystal spec` and `--error-trace`. Read the `inherit_needs` macro in `lib/avram/src/avram/needy_initializer_and_delete_methods.cr` at line 15; done means the failure reports that the class should be abstract instead of the unhelpful missing-types error.

Written by the indexing model from the issue text.