Is your feature request related to a problem? Please describe.

Currently, Zarf's builtins from state are available via the {{ .Variables }} object, but this incidental from how we import all variables and not ideal. Instead, it'd be better to have a dedicated key for these, either .Zarf, .Internal, .State, or some better alternative.

Additional context

Similarly, there's some builtins that aren't included in this map, like registry username! This is a good opportunity to get the state builtins up to date.