Add support for validation of new types

- [x] Collections of **@Validatable** objects *(requires new code-gen template)* | #10
- [ ] Inheritance hierarchies
- [ ] Map
- [ ] Optional
- [ ] Generic **@Validatable** types
- [ ] Primitive types
- [ ] Arrays

Review the remaining checklist items, the @Validatable annotation, and the code-generation template referenced for collections; issue #10 may provide context for the completed work. Define the scope for one or more unchecked types—inheritance hierarchies, Map, Optional, generic @Validatable types, primitive types, or arrays—and consider each supported when validation works for that type.

Written by the indexing model from the issue text.