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.

test/test.einvoice-functionality.ts

@@ -196,4 +196,4 @@ tap.test('EInvoice should export XML correctly', async () => {
 });
 
 // Run the tests
-tap.start();
+export default tap.start();