Improve support for partial registries

[jmrossy]

In order to improve the CLI UX relating to registries and overrides, we'd like the CLI to accept a list of registries, some of which may be full registries but others which may be only partial.

It may be preferable if all the registry tooling was able to treat any registry as 'partial' instead of just PartialRegistry.

https://discord.com/channels/935678348330434570/1328115416488349706/1328525414888378449