### Search before asking - [x] I searched in the [issues](https://github.com/apache/fluss/issues) and found nothing similar. ### Motivation Add NestedRow type support for log table scenarios to handle structured nested data. ### Solution - Extend Arrow row format to support NestedRow type serialization/deserialization - Implement NestedRow type encoding/decoding in client SDK - Add validation for NestedRow type in schema definitions - Ensure end-to-end data flow works for NestedRow type in log tables ### Anything else? _No response_ ### Willingness to contribute - [ ] I'm willing to submit a PR!