Lower dimensional physicals

[simbilod]

A nice feature of the previous iteration of this code was the ability to pass, for instance, 1D objects to a 2D mesh, and have them be conformal and properly tagged as physical. This can replace the current hack for boundary conditions, and allow e.g. sources and monitors to be defined.

This can probably be achieved here with recursive labeled entities

@HelgeGehring

[HelgeGehring]

Sounds great 🥳

[simbilod]

#71 might provide a framework for this; there is some hardcoded dimentionality logic that needs to be fixed first though