Slightly off topic.

"Now, the keyword fast here is saying that the variable fart cannot be changed - it is immutable"

So would this be the same 'fast' as you'd find in 'steadfast' or as in stuck?

Yes, exactly - same Germanic root. "Fast" in Scandinavian languages means firm/fixed/stuck, which is also the original meaning in English (as in "hold fast", "steadfast", "fasten"). The "quick" meaning in English is actually the newer one, derived from the idea of being "stuck" on a course.

Yes. And as in fastness (which would be «fastheit» in Nynorsk): https://www.etymonline.com/word/fastness