v1.2.0

v1.2.0: gmpy2/MPFR backend, python-flint ARB Bessel, parallel evaluation, Fixed Talbot

• Restructure as package (gwr_inversion/) replacing single-file gwr_inversion.py
• Add gmpy2/MPFR backend (~10x speedup on GWR internals, auto-selected when installed)
• Add python-flint/ARB backend for besselk/besseli (~15x speedup on Bessel-heavy transforms)
• Add parallel time-point evaluation via ProcessPoolExecutor (workers= parameter)
• Add Fixed Talbot method wrapper (mpmath.invertlaplace)
• Migrate to pyproject.toml, ruff, strict mypy
• Add pytest regression suite with pre-computed reference data
• Add compare_methods.py benchmark script covering all four test problems

Full Changelog: v1.0.1...v1.2.0