refactor: replace deprecated utf8_encode with mb_convert_encoding

src/Encoder.php

@@ -87,7 +87,7 @@ public function decode(string $text): array
         {
             $new_tokens = array();
             $chars = array();
-            $token = utf8_encode($token);
+            $token = mb_convert_encoding($token, 'UTF-8', mb_list_encodings());
             if(function_exists('mb_strlen'))
             {
                 $len = mb_strlen($token, 'UTF-8');