Configuration validation feedback

Always validate configuration options and provide clear feedback to users about potential issues. This includes warning about unused configuration keys, preventing redundant options, and ensuring cross-platform compatibility.

Key practices:

1. Warn about unused keys: Implement logging for configuration keys that are parsed but not used, helping users identify typos or deprecated settings
2. Avoid redundant options: When designing configuration structures, ensure there’s no ambiguity between None and default enum values - choose one approach consistently
3. Cross-platform validation: Use allow(unused) instead of cfg attributes for configuration fields to prevent warnings on platforms where the feature isn’t available
4. Validate combinations: Require at least one valid option when multiple configuration fields are mutually dependent

Example implementation:

// Warn about unused keys during deserialization
for key in unused.keys() {
    log::warn!(target: LOG_TARGET, "Unused config key: {}", key);
}

// Avoid redundant options - choose Option<T> OR T::Default, not both
pub struct WindowConfig {
    // Good: Clear intent
    pub window_level: WindowLevel, // with Default trait
    
    // Avoid: Ambiguous between None and WindowLevel::Normal
    // pub window_level: Option<WindowLevel>,
}

// Validate required combinations
if !content.hyperlinks && content.regex.is_none() {
    return Err("At least one of hyperlink or regex must be specified");
}

This approach prevents configuration errors that can be difficult to debug and improves the user experience by providing immediate feedback about configuration issues.