feat: add isNode parameter to AST helper methods

- Add optional isNode boolean parameter to all generated helper methods
- When isNode is true, return wrapped object format: { TypeName: instance }
- When isNode is false/undefined, return raw type (backward compatible)
- Update return types to union of Type | { Type: Type }
- Update test snapshots to reflect new signatures

Benefits:
- Maintains backward compatibility (isNode defaults to false)
- Enables programmatic node type identification
- Useful for AST construction with embedded type information
- Type-safe with TypeScript union types

Author: pyramation