Character Option Validator

Create an inputCharOption() method that accepts a Scanner and a String of valid characters. It should:
1. Read input using nextLine()
2. Check if input is exactly 1 character AND is in the validChars string
3. If valid, return the character
4. If invalid, print "ERROR: Character must be one of [validChars]: " and try again

In main(), use it to get Y or N, then display:

You entered: [character]

Example: If user enters "a", "n", then "N", output shows errors then prints the output shown in Expected Output.

⚠️ IMPORTANT - AUTO-INPUT MODE:
This question uses automated input testing. When you run your code, the input stream will AUTOMATICALLY contain: 'N\n'

DO NOT wait for manual keyboard input - Scanner will read from the pre-filled buffer stream immediately. Your validation loop should use scanner.nextLine() to read input.

Think of it like Eclipse/VS Code but with the input already typed in and waiting for your Scanner to read it.