Add unit tests for LoyaltyCard class

[Aglag257]

• Added LoyaltyCardTest to test the parcelable implementation of the LoyaltyCard class
• Implemented tests for the following scenarios:
  • testParcelable: Verifies that LoyaltyCard objects can be correctly serialized and deserialized using Parcel
  • testIsDuplicate_sameObject: Checks that isDuplicate correctly identifies the same object as a duplicate
  • testIsDuplicate_differentObjects: Checks that isDuplicate correctly identifies different objects as not duplicates
  • testToString: Validates the toString method output of LoyaltyCard

This improves test coverage and ensures the correct behavior of the LoyaltyCard class.