REFAC: extract stress/strain/rotation into C APIs and call them from Python

[Dengda98]

• Extract dynamic/static stress, strain, and rotation post-processing into reusable C APIs (grt_compute_* / grt_static_compute_*), with dedicated headers dyn_postprocess.h and static_postprocess.h.
• Expose these APIs through c_interfaces.py and switch Python utils.py helpers to call the C implementations instead of duplicating the tensor formulas in Python. THIS BOOST PYTHON EXECUTION!!!
• Keep CLI modules as thin wrappers over the shared C functions so C and Python paths stay consistent.