Implement filtering of discretization by material IDs

[maxiludwig]

Implement a method to filter the finite element model by specified material IDs. The method should select elements with material IDs matching the given set, and retain only the corresponding nodes, sorting them by their IDs. This enables spatial parameter mapping to be applied only to selected sub-volumes, while other sub-volumes use homogeneous parameters.

[lauraengelhardt]

I this related to .mesh formats? For 4C.yaml files we already have this functionality.