added support for constraints extraction to the dart manager
* fix(datasource): replace getJsonUnchecked with validated getJson in Java, Gradle, Dart, and Flutter datasources Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com> * refactor: remove .nullable() * fix linter errors * chore removed some unused types --------- Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>