Registry types inconsistency

Encoder generate_latest (for example) accepts registry of CollectorRegistry type but it doesn't accept registry of RestrictedRegistry type so it is not consistent. I guess RestrictedRegistry class should inherit CollectorRegistry class because instance of it can be passed to encoders (maybe not only encoders).

Another option is to inherit RestrictedRegistry class from Collector class because CollectorRegistry is inherited from this class, but then anything that accepts CollectorRegistry type should be changed to accept Collector type.

从 generate_latest 编码器入口开始，比较其对 CollectorRegistry 和 RestrictedRegistry 的处理方式。确定注册表类型之间预期的关系，并验证所选择的设计使 RestrictedRegistry 在任何需要 CollectorRegistry 的地方都可以被接受。