Support for compound plugs

We need support for compound plugs. I imagine it to look like in Maya: 

<img width="1390" height="755" alt="Image" src="https://github.com/user-attachments/assets/79be0d51-b912-4c93-a78a-faa0942f8420" />

While the Qt side of things can already be prepared, we have to also ensure that we can properly identify compound plugs in flowpipe itself: https://github.com/PaulSchweizer/flowpipe/issues/180