fix: iterative flattening pass (#4492)

# Description

## Problem\*

Resolves #4449 

## Summary\*

The issue is fixed by implementing an iterative version of the
flattening pass.

## Additional Context



## Documentation\*

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

# PR Checklist\*

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

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Co-authored-by: jfecher <[email protected]>