refactor: replace kontocheck with fintech.iban

[barredterra]

The kontocheck project will be discontinued, so its bank data will no longer be updated. Since v7.9.0, fintech ships its own bank data in fintech.iban. The pinned fintech==7.9.1 already includes it.

Changes

• Remove the kontocheck dependency.
• Use fintech.iban for IBAN validation, bank name and BIC lookup (Bank Account, SEPA Payment Order, create_bank). fintech.iban needs fintech.register(), so each call site calls register_fintech() first. This works without a license key (demo mode).
• Bank Account: the BIC check now also runs for Austrian and Swiss IBANs, because fintech has the bank codes for DE, AT and CH.

Notes

• fintech's check_iban also rejects German IBANs with an unknown bank code.
• Existing Austrian or Swiss Bank Accounts linked to a Bank with a different BIC now fail validation on the next save. The error message names the correct BIC.

[barredterra]

@Mergifyio backport version-15-hotfix

[mergify]

backport version-15-hotfix

✅ Backports have been created

Details

• #458 refactor: replace kontocheck with fintech.iban (backport #457) has been created for branch version-15-hotfix

[greptile-apps]

Confidence Score: 5/5

[Medium risk] Replaces IBAN validation library with a different one.

The PR appears safe to merge, with the previous test gap addressed and no new blocking issues found.

What we checked:

• Matching accounts satisfy required fields: The tests supply both required fields. ERPNext requires a company and accounting account only when is_company_account is enabled; it defaults to disabled here.

_{Reviews (2) · Last reviewed commit: "refactor(test_bank_account): enhance IBA..."}

[barredterra]

🎉 This PR is included in version 16.6.2 🎉

The release is available on GitHub release

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