registry.go
func NewUnstarted(prefix string, tags ...string) *Registry {
	return &Registry{
		instruments: make(map[string]interface{}),
		prefix:      prefix,
		tags:        tags,
	}
}
func NewUnstarted(prefix string, tags ...string) *Registry {
	return &Registry{
		instruments: make(map[string]interface{}),
		prefix:      prefix,
		tags:        tags,
	}
}
// New creates a new Registry without a background flush thread.