Add ability to specify default value for GetOrReadArgument methods

[konard]

Summary

This pull request adds the ability to specify default values for the GetOrReadArgument methods in ConsoleHelpers, addressing issue #66.

🚀 New Features

• GetOrReadArgumentOrDefault(int index, string defaultValue, params string[] args): Simple overload that returns the default value when argument is not found and user provides empty input
• GetOrReadArgumentWithDefault(int index, string readMessage, string defaultValue, params string[] args): Full-featured method with custom prompt message and default value support

✅ Implementation Details

• Backward Compatibility: All existing GetOrReadArgument methods remain unchanged and fully functional
• Smart Default Handling: When an argument is missing from the args array and user provides empty input (or just presses Enter), the specified default value is returned
• Null Safety: Handles null default values gracefully by returning empty string
• Consistent Behavior: Maintains the same string processing (trimming, quote removal) as existing methods

🧪 Testing

• Added comprehensive unit tests covering all scenarios:
  • Existing argument retrieval (should ignore default value)
  • Missing argument with default value
  • Custom message with default value
  • Null default value handling
  • Input processing (quotes, whitespace)

📖 Usage Examples

// Simple usage with default value
var filename = ConsoleHelpers.GetOrReadArgumentOrDefault(0, "default.txt", args);

// Custom message with default value
var timeout = ConsoleHelpers.GetOrReadArgumentWithDefault(1, "Enter timeout in seconds", "30", args);

🔧 Fixes

Closes #66

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