Add Modern Python Features section (3.10+)

[xingarr]

• Add comprehensive coverage of Python 3.10+ features
• Include structural pattern matching examples
• Add union type operator syntax (X | Y)
• Document exception groups and except*
• Add TOML support (tomllib) examples
• Expand type hints with modern syntax
• Include walrus operator patterns
• Add context managers best practices
• Document Task Groups for async programming
• Add Type Parameter Syntax (Python 3.12+)
• Include improved error messages documentation

This enhancement keeps the cheatsheet current with modern Python versions and fills important gaps in coverage.