Add Makefile and switch to uv/hatchling toolchain
- Add Makefile with install, test, ci, format, and clean targets
- Switch build backend from setuptools to hatchling
- Add ruff and pytest as dev dependencies
- Configure ruff (line-length=100, py39) and pytest (test/ dir)
- Auto-fix ruff formatting and lint issues in plc_register.py
- Add .ruff_cache/ to .gitignore
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>