Add support for calling Zig functions

[Luukdegram]

• Add compiler support for 'packages' for type support. (compiler doesn't know anything about this package, therefore we should ignore type checking for those cases but return a general .module type or something like that).
• Add function to value.zig to wrap a Zig function into a Luf Value.
• Add VM support to add Zig functions as a 'package'.