Avoid using Linq where a more performant alternative is readily available.

src/Renci.SshNet/Sftp/SftpFileAttributes.cs

@@ -417,7 +417,7 @@ namespace Renci.SshNet.Sftp
                 throw new ArgumentOutOfRangeException("mode");
             }
 
-            var modeBytes = mode.ToString(CultureInfo.InvariantCulture).PadLeft(3, '0').ToArray();
+            var modeBytes = mode.ToString(CultureInfo.InvariantCulture).PadLeft(3, '0').ToCharArray();
 
             var permission = (modeBytes[0] & 0x0F) * 8 * 8 + (modeBytes[1] & 0x0F) * 8 + (modeBytes[2] & 0x0F);