[gmp007]

Summary

• replace the removed scipy.integrate.trapz import with trapezoid
• validate Birch-Murnaghan fit inputs before calling curve_fit so too-few data points produce a clear message instead of an uncaught SciPy error
• add lightweight unittest and CI checks that do not install the full scientific/ML dependency stack

Testing

• python3 -m unittest discover -s tests
• python3 -m py_compile src/process_stress.py

Addresses #5.