Add testing materials for Module 12: Testing Fundamentals

- Created a multiple-choice quiz (task1.md) covering unit testing concepts.
- Developed a comprehensive testing suite for a Calculator class (task2.md) including:
  - Implementation of basic arithmetic operations and advanced functions.
  - Unit tests using JUnit 5 with various test structures (basic, nested, parameterized).
  - Performance and edge case tests to ensure robustness.
  - A test suite runner for executing tests programmatically.
  - Bonus tasks for enhanced testing practices.

Author: Omar-Mega-Byte