🎉 Major Release - Complete Modernization

This is a major release representing a complete modernization of the heatfall package with significant improvements in reliability, functionality, and maintainability.

Key Features:
- Multiple color schemes (distinct, random, wheel)
- Enhanced Context class extending landfall.Context
- Comprehensive type annotations and input validation
- Modern pyproject.toml packaging
- 100% test coverage across Python 3.8-3.13
- Full development infrastructure (ruff, mypy, tox)

Breaking Changes:
- Now built on top of landfall>=0.4.0
- Removed custom density_colors() function
- Simplified Context class by extending landfall.Context
- Removed unused plotting functions

Migration:
- Install landfall: pip install landfall>=0.4.0
- Use color_scheme parameter instead of custom colors
- Basic function calls remain backward compatible