Function segment_cjk 

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

Insert a space after every CJK character so whitespace tokenization treats each CJK character as a separate token. Latin/digit/punctuation runs and existing whitespace are left untouched.

Examples: "知識グラフ" → "知 識 グ ラ フ ", "rust ownership" → "rust ownership", "Rustで非同期" → "Rust で 非 同 期 ".