feat(packaging): modernize packaging with pyproject.toml, extras, and CI

[cto-new]

Summary

This change introduces modern packaging and CI tooling for Frackture, including a PEP 621 compliant pyproject.toml, optional extras, and a CI workflow.

Details

• Add pyproject.toml with metadata, dependencies, and setuptools-scm versioning
• Move requirements into dev/benchmark extras and enable editable installs
• Create a proper package layout under src/frackture and a minimal CLI entry
• Introduce a Makefile for build/publish tasks
• Add GitHub Actions workflow for lint, tests, and optional benchmarks on pushes/tags
• Provide RELEASE.md with release process and PyPI publishing notes
• Update README with development/install guidance
• Ensure compatibility with legacy module frackture (2).py