008e9c395a
Replace the silent (long) cast with an explicit fractional check: if value * factor has a non-zero remainder, TryParseIn/TryParseCoins return false. The caller already shows "Importo non valido." to the user, so no UI change is needed. Covers TryParseIn (all units) and TryParseCoins. Adds CoinAmountTests with valid and invalid cases including the triggering example (1.9 sat).