FieldType DecimalItem may fail with a TypeError in preSave

Problem/Motivation

I wonder about strict types in the context of \Drupal\Core\Field\Plugin\Field\FieldType\DecimalItem::preSave. It calls

round($this->value, $this->getSetting('scale'))

which throws a TypeError exception on PHP 8.3 and later if $this->value happens to be a string. This can happen easily if a module calls ->setValue($value) and where $value may be a string, like e.g. received from a custom form or an external API.

Steps to reproduce

• Create a decimal field with the name field_decimal on a node entity type
• Write some PHP custom code like this and see that failing:
  

  $node = Node::load(1);
  $node->set('field_decimal', '2.5');
  $node->save();
  

Similar code can be found in contrib and custom code all over the place, still it is theoretical and I can't provide any more realistic examples.

Proposed resolution

Type casting the value before being passed to the round method.