nightly-2024-05-19: feat: do not return databus returndata, keep it private. (#5023)

# Description

## Problem\*

Related to  #4974

## Summary\*
Very small PR which avoids returning databus objects, because they need
to be handled as private inputs.
This is incremental work, so it cannot be tested yet. The PR only impact
databus use case.



## Additional Context



## Documentation\*

Check one:
- [X] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [ ] I have tested the changes locally.
- [X] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.