Add thread-safe Singleton implementation with comprehensive tests

[Harsh2806]

• Implement SingletonBase metaclass for thread-safe singleton pattern
• Add wrt_singleton.py module with reusable singleton implementation
• Add comprehensive thread-safety tests in test_singleton_threadsafe.py
• Integrate singleton pattern into patcher.py for genetic algorithm optimization

[Harsh2806]

Hi @52North/maintainers, I've submitted this PR to address the thread-safety issue in the SingletonBase implementation (#76).

The changes include:

• A thread-safe metaclass using double-checked locking pattern
• Comprehensive unit tests validating thread-safety with multiple concurrent threads
• Updated documentation reflecting the thread-safe implementation
• Integration with the existing patcher.py module for genetic algorithm optimization

The implementation maintains backward compatibility with existing code using SingletonBase. Please review the changes and let me know if you have any suggestions or questions.

Thanks!