feat: Implement PEPPOL and XRechnung validators for compliance with e-invoice specifications

- Added PeppolValidator class to validate PEPPOL BIS 3.0 invoices, including checks for endpoint IDs, document type IDs, process IDs, party identification, and business rules.
- Implemented validation for GLN check digits, document types, and transport protocols specific to PEPPOL.
- Added XRechnungValidator class to validate XRechnung 3.0 invoices, focusing on German-specific requirements such as Leitweg-ID, payment details, seller contact, and tax registration.
- Included validation for IBAN and BIC formats, ensuring compliance with SEPA regulations.
- Established methods for checking B2G invoice indicators and validating mandatory fields for both validators.

ts/formats/converters/xml-to-einvoice.converter.ts

@@ -25,29 +25,45 @@ export class XMLToEInvoiceConverter {
   public async convert(xmlContent: string, format: 'UBL' | 'CII'): Promise<EInvoice> {
     // For now, return a mock invoice for testing
     // A full implementation would parse the XML and extract all fields
-    const mockInvoice: EInvoice = {
+    const mockInvoice = {
       accountingDocId: 'TEST-001',
       accountingDocType: 'invoice',
       date: Date.now(),
       items: [],
       from: {
+        type: 'company' as const,
         name: 'Test Seller',
+        description: 'Test Seller Company',
         address: {
-          streetAddress: 'Test Street',
+          streetName: 'Test Street',
+          houseNumber: '1',
           city: 'Test City',
           postalCode: '12345',
+          country: 'Germany',
           countryCode: 'DE'
+        },
+        registrationDetails: {
+          companyName: 'Test Seller Company',
+          registrationCountry: 'DE'
         }
-      },
+      } as any,
       to: {
+        type: 'company' as const,
         name: 'Test Buyer',
+        description: 'Test Buyer Company',
         address: {
-          streetAddress: 'Test Street',
+          streetName: 'Test Street',
+          houseNumber: '2',
           city: 'Test City',
           postalCode: '12345',
+          country: 'Germany',
           countryCode: 'DE'
+        },
+        registrationDetails: {
+          companyName: 'Test Buyer Company',
+          registrationCountry: 'DE'
         }
-      },
+      } as any,
       currency: 'EUR' as any,
       get totalNet() { return 100; },
       get totalGross() { return 119; },
@@ -100,7 +116,7 @@ export class XMLToEInvoiceConverter {
       console.warn('Error parsing XML:', error);
     }
     
-    return mockInvoice;
+    return mockInvoice as EInvoice;
   }
   
   /**