feat: add hello world script with tests

[Wirasm]

Summary

Adds a simple hello.py script to the root directory of the Dylan project for testing Python execution and demonstrating basic script structure. The implementation follows the project's KISS principle by creating the simplest possible working script with proper Python conventions.

Changes

• Add hello.py script with type hints and Google-style docstrings
• Add comprehensive unit tests in tests/test_hello.py
• Add PRP documentation in PRPs/features/completed/add-hello-world.md

Implementation Details

This implementation follows the Product Requirement Prompt defined in PRPs/features/completed/add-hello-world.md.

The hello.py script:

• Prints "Hello, World!" to the console
• Follows Python best practices with type hints and docstrings
• Can be executed directly with uv run python hello.py
• Includes a shebang line for direct execution on Unix systems
• Adheres to all project code quality standards (ruff, mypy, black)

Testing

• All existing tests pass
• New unit tests added in tests/test_hello.py
• Manual testing completed - script executes successfully
• All validation commands pass (ruff, mypy, pytest)

Files Changed

• PRPs/features/completed/add-hello-world.md (204 additions)
• hello.py (29 additions)
• tests/test_hello.py (49 additions)

Total: 282 additions across 3 files