[CH][SEPA CT] Export requires both IBAN and Clearing No. for domestic payments and refunds

[dcenic]

Swiss SEPA CT Export requires both IBAN and Clearing No. for domestic payments and refunds

Expected:
If Clearing No. is blank, it can be extracted from IBAN (IBAN contains it).

What & why

Added the logic that extracts Clearing No. from IBAN, and using it when determining the payment type, and when exporting to MmbId in the SEPA CT file.

Linked work

Fixes AB#646497

How I validated this

• I read the full diff and it contains only changes I intended.
• I built the affected app(s) locally with no new analyzer warnings.
• I ran the change in Business Central and confirmed it behaves as expected.
• I added or updated tests for the new behavior, or explained below why none are needed.

What I tested and the outcome (required — be specific: scenarios, commands, screenshots for UI changes)

Risk & compatibility

• Vendor payment + clearing: identical output → zero risk.
• Customer refund / vendor-blank-clearing: old output was either invalid (MmbId = IBAN) or nonexistent (errored), so there's nothing valid to break; the fix only makes MmbId schema-correct.
  Since CdtrAcct/IBAN is unchanged and is what routes, no in-flight payment behavior changes — only the redundant MmbId becomes correct.