Made Decoder::castInteger() final

The method never needs to be overridden and it allows the optimizer to skip some type checking

src/Decoder.php

@@ -66,7 +66,7 @@ final protected function __construct(protected readonly string $bencoded)
 	/**
 	* Cast given string as an integer and check for clamping
 	*/
-	protected function castInteger(string $string, int $clamp): int
+	final protected function castInteger(string $string, int $clamp): int
 	{
 		$value = (int) $string;
 		if ($value === $clamp && !is_int(+$string))