nightUtxoJsonProvider

Live NIGHT-UTXO list (as the registration-filter JSON) wired by MidnightSdk. Lets balance/balanceFlow compute dustRegistered from true per-UTXO registration state — "are all current NIGHT UTXOs generating dust?" — instead of the dust>0 heuristic (#265). Null → fall back to the heuristic (e.g. before the SDK wires it).