Function text_collapse 

pub fn text_collapse(text: &str) -> String

Normalize and simplify text for similarity hashing.

Applies NFD normalization, lowercasing, removes whitespace and characters in Unicode categories C (control), M (mark), and P (punctuation), then recombines with NFKC normalization. Mirrors the reference text_collapse step for step; Unicode data comes from the tables the dependencies ship.