GreatCell benchmark suite HYDRO_MECHANICS_WITH_LIE

This merge request adds Phase 2 of the GreatCell benchmark suite (DECOVALEX‑2027). It includes a new Jupyter notebook demonstrating hydro‑mechanical simulations of intact and fractured samples with OGS’s HYDRO_MECHANICS and HYDRO_MECHANICS_WITH_LIE processes. Mesh generation, simulation runs (for various load cases and materials), and post‑processing are all handled by clean, reusable Python classes. Phase 1 covered purely mechanical deformation—see !5297 (merged)—and Phase 3 provides VPF results.