Duplicated code in user input interpreter class

Several different methods in the Project0.ConsoleApp.ConsoleInputInterpreter class use repeated logic for input validation, these can be simplified and improve readability of the class with the addition of some helper methods.

Examine the Project0.ConsoleApp.ConsoleInputInterpreter class to identify repeated validation logic across methods. Look for patterns that can be extracted into private helper methods. Run existing tests to ensure refactoring does not break functionality. The goal is to simplify the class and improve readability without changing external behavior.

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