title: library_private_types_in_public_api and StatefulWidget
body: <p>After upgrade the linter to the new version (<code>flutter_lints: 2.0.1</code>) in my pubspec
  the linter enables this rule:
  <a href="https://dart.dev/tools/linter-rules#library_private_types_in_public_api" rel="noreferrer">library_private_types_in_public_api</a> by default. I don't understand why. In my App project there are a lot of widget classes extended by <code>StatefulWidget</code>. The state class is always private. <a href="https://api.flutter.dev/flutter/widgets/StatefulWidget-class.html" rel="noreferrer">Example</a> projects do it the same way. Can someone explain why this rule make sense?</p>
  <p>Btw.: I know i can disable this rule.</p>