[WIP] Fix credit note builder to respect XML format

[Copilot]

• Fix credit note builder to match PEPPOL BIS 3.0 CreditNote format:
  • Remove unused xmlns:cec namespace from CreditNote root element (not in PEPPOL standard)
  • Remove UBLVersionID element (not in PEPPOL BIS 3.0 standard examples)
  • Remove unnecessary fallback values for ID, creditNoteTypeCode, documentCurrencyCode
  • Add support for optional fields in builder: note, accountingCost, taxCurrencyCode, taxPointDate, invoicePeriod
• Apply same fixes to invoice builder for consistency (remove xmlns:cec, UBLVersionID, add optional fields)
• Update schemas if needed for PEPPOL compliance
• Update existing tests to match new output format
• Add new tests for credit note builder optional fields
• Verify all tests pass

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 0 complexity . 0 duplication

Metric	Results
Complexity	0
Duplication	0

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