feat(validation): Implement EN16931 compliance validation types and VAT categories

- Added validation types for EN16931 compliance in `validation.types.ts`, including interfaces for `ValidationResult`, `ValidationOptions`, and `ValidationReport`.
- Introduced `VATCategoriesValidator` in `vat-categories.validator.ts` to validate VAT categories according to EN16931 rules, including detailed checks for standard, zero-rated, exempt, reverse charge, intra-community, export, and out-of-scope services.
- Enhanced `IEInvoiceMetadata` interface in `en16931-metadata.ts` to include additional fields required for full standards compliance, such as delivery information, payment information, allowances, and charges.
- Implemented helper methods for VAT calculations and validation logic to ensure accurate compliance with EN16931 standards.

ts/interfaces/common.ts

@@ -44,6 +44,7 @@ export interface ValidationError {
 export interface ValidationResult {
   valid: boolean; // Overall validation result
   errors: ValidationError[]; // List of validation errors
+  warnings?: ValidationError[]; // List of validation warnings (optional)
   level: ValidationLevel; // The level that was validated
 }