Auto review - 1

Summary by Bito

• Introduces a brand-new file that implements user management functionality with multi-threading and inheritance, including methods to process user data.
• Improves encapsulation in the test.java file by changing public fields to private and updating naming conventions to adhere to best practices.
• Adds testing code to verify the new functionality.
• Overall summary: Introduces and refactors user management functionality with multi-threading, inheritance, and testing elements while improving encapsulation and code maintainability, laying groundwork for further enhancements in handling user operations.