- `DSLDirective` class: Represents GraphQL directives with argument validation and AST generation
- `DSLDirectable` mixin: Provides reusable `.directives()` method for all DSL elements that support directives
- `DSLFragmentSpread` class: Represents fragment spreads with their own directives, separate from fragment definitions
- Executable directive location support on query, mutation, subscription, fields, fragments, inline fragments, fragment spreads, and variable definitions ([spec](https://spec.graphql.org/October2021/#sec-Type-System.Directives))
- Automatic schema resolution: Fields automatically use their parent schema for custom directive validation
- Fallback on builtin directives: Built-in directives are still available if a schema is not available to validate against

The implementation follows the [October 2021 GraphQL specification](https://spec.graphql.org/October2021/) for executable directive locations and maintains backward compatibility with existing DSL code. Users can now use both built-in directives (`@skip`, `@include`) and custom schema directives across all supported GraphQL locations.

Co-authored-by: Leszek Hanusz <[email protected]>