feat: Implement high-priority code improvements

[adwaitas28]

• Add comprehensive type hints to Array and BankAccount classes
• Replace print statements with proper exception handling
• Create detailed docstrings with examples and parameter descriptions
• Implement complete unit test suite using pytest framework
• Add modern Python features (f-strings, Decimal, custom exceptions)
• Create project infrastructure (requirements.txt, pytest.ini, test runner)

Improved files:

• Programs/P30_Array.py: Enhanced with proper error handling and type safety
• OOP/P09_BankAccount.py: Added financial precision and robust validation
• tests/test_array.py: 50+ comprehensive test cases
• tests/test_bank_account.py: 60+ business logic test cases
• requirements.txt: Development and testing dependencies
• pytest.ini: Test configuration with coverage reporting
• run_tests.py: Demonstration script for improved functionality

These changes transform educational code into production-ready, maintainable Python following modern best practices.