Normalize a Japanese address (to town level) / 住所の正規化（町域まで）

Split a Japanese address into prefecture, city, town and the rest (block numbers, building), matching Japan Post's address data, and return candidate postal codes. Absorbs full/half-width, spacing, kanji vs. arabic numerals, ヶ/ケ and omitted county names; fills in the prefecture when the city is unique. Does NOT verify block/house numbers and has no coordinates. level tells how far the match went: 0 = nothing matched, 1 = prefecture only (see city_candidates if the city name is ambiguous), 2 = city matched but not the town (postal_codes are city-wide candidates), 3 = town matched. address and municipality_code are null below level 2. flags: partial (level below 3), ambiguous (several city or postal code candidates — ask the user or show all). / 住所を都道府県・市区町村・町域・残り（番地・建物名など）に分け、郵便番号の候補を返す（日本郵便のデータにあてはめる）。番地が実在するかの確認と緯度・経度はない。level：0＝わからない、1＝都道府県まで、2＝市区町村まで（町域はわからない）、3＝町域まで。