chore(deps): update dependency source_gen to v4

Author: renovate[bot]

forui_internal_gen/pubspec.yaml

@@ -19,7 +19,7 @@ dependencies:
   collection: ^1.18.0
   dart_style: ^3.0.1
   meta: ^1.16.0
-  source_gen: ^3.0.0
+  source_gen: ^4.0.0
 
 dev_dependencies:
   build_test: ^3.3.2