Proper Option type usage

// Good: Truly optional value
struct Config {
    refresh_interval: Option<Duration>,  // May not be configured
    error_message: Option<String>        // Only present on error
}

// Bad: Using Option when value is never None
struct AuthInterceptor {
    tenant_id: AsciiMetadataValue,
    shard_id: Option<AsciiMetadataValue>  // If always present, remove Option
}

// Bad: Using empty string instead of Option
struct Settings {
    base_url: String  // Empty string is meaningless, use Option<String>
}