Add surface and line integral support (PETSc-backed) in UW for fault-based models

[gthyagi]

Underworld3 currently supports volume integrals through PETSc/DMPlex, but there is no native support for surface or line integrals over embedded lower-dimensional entities (e.g., fault surfaces or intersection curves).

This is increasingly important for explicit fault modelling in geodynamics, where we need to compute:
• Surface integrals of traction, stress, or slip over fault planes
• Line integrals along fault intersections or triple junctions
• Interface fluxes or energy budgets across internal discontinuities

Note: Prioritise Line Integral Support

Requesting implementation of native, PETSc-backed line integral support in Underworld3, specifically to enable accurate replication of the Barr & Houseman benchmark configurations.