Directly generate pdfpc config

[Beiri22]

It might not be 100% perfect by now, but please have a look, should fix #83 . As I see now, there is no big logic to fear.

Known problems:

• Empty page at end. This might be cause by emitting the metadata, but i think Introduce second variant of Ignorant Behaviour and prevent weak page breaks at basically empty pages typst/typst#1929 shall fix this.

How to use:

$ typst query gauss.typ "<pdfpc>" --field value --one > gauss.pdfpc

Right now, every theme does emit the metadata separately.
Maybe we could introduce a base theme that is used by all others
to centralize tasks and settings that all themes share?

[Beiri22]

I really like rust, but have you considered creating the pdfpc file directly without a rust program?