Expands variable validation to also include support for partial resolution.
In short, this will partially execute script code until it hits unresolved runtime variables, and store that as the new script representation. This functionality will allow for the upcoming `inspect` command, which will show users their script code in action without having to dry-run.
Adds generic `filter_include` and `filter_exclude` plugins in anticipation for function script usage. Will detail it more with official docs at a later time!
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.
