[WIP] chore: use foundry

[fubhy]

trafficstars

This is a work in progress and serves as an experiment / exploration first and foremost. If successful, feel free to (but by no means obliged to) consider this for merging.

As foundry is still in its infancy and the internal integration tests are mostly based on rather simple & flat contract repositories this is a good way to explore UX/DX shortcomings within foundry for slightly more involved contract hierarchies.