Fix CSV import rounding errors with exchange rates (#5069)

[funnym0nk3y]

This commit addresses issue #5069 where CSV imports fail validation due to rounding errors when dealing with foreign exchange rates.

Changes made:

1. BaseCSVExtractor.java:

   • Replaced Math.round(BigDecimal.doubleValue()) with BigDecimal.setScale(0, RoundingMode.HALF_UP).longValue()
   • This avoids precision loss from converting BigDecimal to double
   • Applies to both extractGrossAmount() and createGrossValueIfNecessary()

2. CheckForexGrossValueAction.java:

   • Added tolerance of ±2 (±0.02 in currency) to validation
   • This accounts for unavoidable rounding when Money values are limited to 2 decimal places
   • Prevents false positives while still catching actual errors

Root cause: Money stores amounts as longs with 2 decimal precision (factor of 100). When gross amounts are calculated with exchange rates, rounding to 2 decimals can cause small discrepancies that fail strict equality checks.

Example from issue:

• Value: 95.26 CAD, FX Rate: 1.3795
• Calculated: 95.26 / 1.3795 = 69.0540... → rounded to 69.05
• Recalculated: 69.05 × 1.3795 = 95.254... → 95.25 ≠ 95.26

The fix improves calculation precision and adds reasonable tolerance.

[buchen]

I'll have a look - I also need to rebase because I just happen to touch that close (deriving the exchange rate if it is not present).

And a test case helps to avoid breaking this feature in the future.