De-duplicate a list of records or strings. Exact: group by a `key` field (dot-path) or, by default, the whole item (key-order-insensitive). Fuzzy (`fuzzy`: a field name, or true for scalar strings): group by normalized Levenshtein similarity ≥ `threshold` (default 0.85) — e.g. 'Jean Dupont' ≈ 'jean dupont' but 'Jean Martin' stays separate. Returns unique[] and duplicates[] (kept + dropped indices). Fuzzy ≤ 1000 items.