FINERACT-2523: Fix inconsistent interest recalculation for cumulative loans with floating rates

[DeathGun44]

Description

LoanApplicationTerms.updateAnnualNominalInterestRate() did not invalidate the cached fixedEmiAmount when the interest rate changed. This caused exact repayments on cumulative loans with floating rates to only adjust the last installment, while overpayments correctly recalculated all future installments.

Fix: Reset fixedEmiAmount = null when the annual nominal interest rate actually changes, forcing EMI recalculation for all subsequent installments.

Added integration test to verify the fix with both exact repayment and overpayment scenarios.

Checklist

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