Implement Nested Steps Functionality

[skyelaird]

This commit addresses all remaining items from NEXT_STEPS.md to prepare for public PyPI release:

Performance Analysis:

• Add profile_performance.py for systematic performance profiling
• Validate performance targets: 0.009s per prediction (111x faster than 1s target)
• Area coverage: 0.78s for 100 predictions (38x faster than 30s target)
• Identify optimization opportunities (ionospheric profile computation)

Release Preparation:

• Create CHANGELOG.md with version history and release template
• Update pyproject.toml to v0.9.0 (Beta status)
• Enhance package metadata with comprehensive keywords
• Configure proper README rendering for PyPI

Community Infrastructure:

• Add GitHub issue templates (bug report, feature request)
• Add comprehensive pull request template with validation checklist
• Include testing requirements and performance benchmarks

Documentation:

• Create notebooks/01_basic_prediction.ipynb with complete examples
• Include frequency scanning, 24-hour time analysis, and visualization
• Add interpretation guidelines for SNR, reliability, and MUF
• Provide hands-on exercises for users

Current Status:

• Validation: 86.6% pass rate (226/261 tests) - EXCEEDS 85% target
• Performance: All targets exceeded by >38x
• Ready for public beta release

Next Steps:

• Optional: Add type hints to core modules (Sphinx documentation)
• Optional: Performance optimizations (already exceeds targets)
• Potential: Improve test pass rate from 86.6% to 90% (edge cases)