Reward value

[Ayushsaw11]

This is the first Commit of given task.

[Ayushsaw11]

I implemented the RewardValue class to handle conversions between cash and miles. The class includes two constructors: one for converting cash to miles and another for converting miles to cash. We also added methods to retrieve the cash and miles values. To ensure the correctness of the class, we wrote unit tests using JUnit 5, covering scenarios such as creating objects with cash or miles values and validating the conversions from cash to miles and vice versa. Finally, we used assertions in the tests to confirm that the conversion logic works correctly.