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/plugins.ts

@@ -22,8 +22,12 @@ import {
 
 // XML-related imports
 import { DOMParser, XMLSerializer } from 'xmldom';
+import * as xmldom from 'xmldom';
 import * as xpath from 'xpath';
 
+// XSLT/Schematron imports
+import * as SaxonJS from 'saxon-js';
+
 // Compression-related imports
 import * as pako from 'pako';
 
@@ -49,8 +53,12 @@ export {
   // XML-related exports
   DOMParser,
   XMLSerializer,
+  xmldom,
   xpath,
   
+  // XSLT/Schematron exports
+  SaxonJS,
+  
   // Compression-related exports
   pako,