Completely rewrite how subscription validation is performed. Optimizes it quite a bit while also adding backend support for the upcoming `dissect` sub-command, where you can resolve any subscription into its 'raw' form for easier debugging when making scripting changes.
A complete gutting of the internals of ytdl-sub to support functions in our variable syntax, in addition to being able to access a yt-dlp entry's .info.json fields using functions. Functionally, ytdl-sub should still look and behave the same from a user-perspective.
With so many lines of code changed (+8927, -2708), no doubt there will be new issues. Please make a GH issue or reach out on Discord if your config/subscriptions break in any way/shape/form.
Details on how to use function support will come soon in the form of proper documentation in our readthedocs.
