refactor(registry): improve constructors of Registry

[koushiro]

The current APIs of Registry does not allow me to change the prefix and labels of a Registry after it's constructed.

Breaking Changes:

• change fn with_prefix(prefix: ...) -> Self => fn with_prefix(mut self, prefix: ...) -> Self
• change fn with_labels(labels: ...) -> Self => fn with_labels(mut self, labels: ...) -> Self
• remove fn with_prefix_and_labels(prefix: ..., labels: ...) -> Self

[koushiro]

BTW, I think the sub_registry part is not very useful, and it might be better to remove these sub_registry_* APIs to keep the Registry APIs simple (as long as the prefix and labels field of the registry are exposed, downstream users can implement these functionalities by themselves)