Fix precision loss when rounding large integers in NumberToLocalizedStringTransformer

Add type check in `round()` method to bypass rounding for integer values,
preventing precision loss for large integers that are still below PHP_INT_MAX.

🤖 Generated with [Claude Code](https://claude.ai/code)

Author: OskarStark

src/Symfony/Component/Form/Extension/Core/DataTransformer/NumberToLocalizedStringTransformer.php

@@ -189,6 +189,10 @@ protected function castParsedValue(int|float $value): int|float
      */
     private function round(int|float $number): int|float
     {
+        if (\is_int($number)) {
+            return $number;
+        }
+
         if (null !== $this->scale && null !== $this->roundingMode) {
             // shift number to maintain the correct scale during rounding
             $roundingCoef = 10 ** $this->scale;

src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/NumberToLocalizedStringTransformerTest.php

@@ -726,4 +726,33 @@ public static function eNotationProvider(): array
             [1232.0, '1.232e3'],
         ];
     }
+
+    public function testReverseTransformDoesNotCauseIntegerPrecisionLoss()
+    {
+        $transformer = new NumberToLocalizedStringTransformer();
+
+        // Test a large integer that causes actual precision loss when cast to float
+        $largeInt = \PHP_INT_MAX - 1; // This value loses precision when cast to float
+        $result = $transformer->reverseTransform((string) $largeInt);
+
+        $this->assertSame($largeInt, $result);
+        $this->assertIsInt($result);
+    }
+
+    public function testRoundMethodKeepsIntegersAsIntegers()
+    {
+        $transformer = new NumberToLocalizedStringTransformer(2); // scale=2 triggers rounding
+        
+        // Use reflection to test the private round() method directly
+        $reflection = new \ReflectionClass($transformer);
+        $roundMethod = $reflection->getMethod('round');
+        $roundMethod->setAccessible(true);
+        
+        $int = \PHP_INT_MAX - 1;
+        $result = $roundMethod->invoke($transformer, $int);
+        
+        // With the fix, integers should stay as integers, not be converted to floats
+        $this->assertSame($int, $result);
+        $this->assertIsInt($result);
+    }
 }