List sub-wallets, optionally filtered by currency or uid. Broad searches return an array and may include an opaque lek; send that value back unchanged for the next page. Supplying both currency and uid performs an exact lookup and returns one sub-wallet object instead of an array. Surrounding spaces in uid are ignored, but letter case is preserved. A UID identifies your customer within a currency, so retain both values when mapping wallets. An exact lookup returns HTTP 404 when no wallet matches.