Rearchitect lazy loading registry cache

[jromero]

Side tantrum: I have issues with the architecture decision. I'm not seeing the value of lazy loading the cache in this case. I think a better pattern may be to differentiate between a RegistryCache "config" and an "initialized" RegistryCache. Any time a RegistryCache is provided it should already be initialized. A RegistryCacheConfig can be used in cases where we just want to provide configuration without necessary interaction.

Originally posted by @jromero in #782 (comment)

[dfreilich]

big big 👍 to this. I found the registry cache code very hard to test comprehensively, because of the lazy loading.