Allow negative VAT values

Author: Copilot

src/MallPay/Vat.php

@@ -4,14 +4,12 @@
 
 use SlevomatCsobGateway\Currency;
 use SlevomatCsobGateway\Encodable;
-use SlevomatCsobGateway\Validator;
 
 class Vat implements Encodable
 {
 
 	public function __construct(private int $amount, private Currency $currency, private int $vatRate)
 	{
-		Validator::checkNumberPositiveOrZero($amount);
 	}
 
 	/**

tests/unit/MallPay/VatTest.php

@@ -2,7 +2,6 @@
 
 namespace SlevomatCsobGateway\MallPay;
 
-use InvalidArgumentException;
 use PHPUnit\Framework\TestCase;
 use SlevomatCsobGateway\Currency;
 
@@ -16,14 +15,4 @@ public function testEncode(): void
 		self::assertSame(['amount' => 123, 'currency' => 'USD', 'vatRate' => 15], $vat->encode());
 	}
 
-	public function testValidation(): void
-	{
-		try {
-			new Vat(-123, Currency::USD, 15);
-			self::fail();
-		} catch (InvalidArgumentException $e) {
-			self::assertSame('Value is negative.', $e->getMessage());
-		}
-	}
-
 }