Use a dedicated relationship model and enable dataclass support

[armanddidierjean]

Description

Please explain the changes you made here.

Checklist

• [ ] Created tests which fail without the change (if possible)
• [ ] All tests passing
• [ ] Extended the documentation, if necessary

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 81.55%. Comparing base (64d404b) to head (ec11183).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #606 +/- ## ======================================= Coverage 81.54% 81.55% ======================================= Files 128 128 Lines 9929 9933 +4 ======================================= + Hits 8097 8101 +4 Misses 1832 1832 ```

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