discover.go
func WithUserAgent(agent string) Option {
	return func(d *Discover) error {
		d.userAgent = agent
		return nil
	}
}
func WithUserAgent(agent string) Option {
	return func(d *Discover) error {
		d.userAgent = agent
		return nil
	}
}
// WithUserAgent allows specifying a custom user agent option to send with
// requests when the underlying client library supports it.