Add Unit and UI Tests to Existing Test Files

[mentatbot[bot]]

• Added unit tests to TodoCoreDataExampleTests.swift for core functionalities including adding, removing, and completing todo items.
• Added UI tests to TodoCoreDataExampleUITests.swift for basic UI interactions such as adding, completing, and deleting todo items.
• Updated TodoCoreDataExampleUITestsLaunchTests.swift to include a test for the initial launch state of the app.
• Ensured all tests can be run using Xcode's standard test runner (Cmd+U) and followed Swift best practices for unit and UI testing.

Closes #1