[WIP] Migrate addons/br/nfe and addons/br/nfse to new rules package

[Copilot]

• Fetch and merge latest rules branch commits (fix expr package)
• Migrate addons/br/nfe package from validation to rules
  • Rewrite bill_invoices.go with rules-based invoice, party, address rules
  • Rewrite bill_line.go with rules for required tax categories
  • Rewrite pay.go with rules for payment instructions/advance
  • Update nfe.go: add rules.RegisterWithGuard, remove Validator field
  • Update test files to use rules.Validate() and new error messages
• Migrate addons/br/nfse package from validation to rules
  • Rewrite bill_invoices.go with rules-based invoice, supplier, address rules
  • Rewrite bill_line.go with rules for required tax categories
  • Rewrite org_item.go with rules for item extensions
  • Rewrite tax_combo.go with rules for tax combo extensions
  • Update nfse.go: add rules.RegisterWithGuard, remove Validator field
  • Update test files to use rules.Validate() and new error messages
• Run tests and verify all pass

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[samlown]

This was already done directly in the repo.