refactor: use lib.generators.toPlist

[z0al]

The PR:

• Got rid of our custom lib. I hated manual imports on every file.
• Introduces the use of lib.generators.toPlist to generate an .plist file per domain that can then be imported via defaults import <domain> <file>
• Update the test setup to account for ☝🏻 . I'm doing some surgical rg -> jc --plist -> jq on the test helpers but it all works fine. I even managed to come up with a DSL-like syntax that I like a lot e.g.

Domain <domain>      # Sets context for the follow-up "Set" and "Del" asserts.
Set <attr> <value>   # Asserts the <attr> is set with given <value>
Del <attr>           # Asserts the <attr> is deleted