Closure table for AttributeSet DAG hierarchies.

Enables composition and inheritance between attribute sets:

• includes — composition: child attributes are added to parent
• extends — inheritance: child specialises parent
• overrides — explicit override of specific attributes

Merge strategies

When attribute sets compose, handle collisions are resolved by:

• parent_wins — parent's config takes precedence
• child_wins — child's config takes precedence
• merge — deep merge of configs

Override config

Allows fine-grained override of individual attribute handles:

%{"email" => %{"required" => true}, "phone" => %{"visible" => false}}