perf: bound NWC response replay and memoize the countdown state lookup

lib/features/trades/screens/trade_detail_screen.dart

@@ -1136,8 +1136,23 @@ class _CountdownWidget extends ConsumerWidget {
 
   /// Find the message that triggered the current state
   /// Returns null if no valid message is found
+  /// Memo per history-list instance: the index emits a new list only on real
+  /// changes, while the 1 s countdown tick rebuilds with the same instance —
+  /// the copy+sort below used to run every second.
+  static final Expando<Map<Status, MostroMessage?>> _stateMessageMemo =
+      Expando();
+
   MostroMessage? _findMessageForState(
       List<MostroMessage> messages, Status status) {
+    final memo = _stateMessageMemo[messages] ??= {};
+    if (memo.containsKey(status)) return memo[status];
+    final result = _findMessageForStateUncached(messages, status);
+    memo[status] = result;
+    return result;
+  }
+
+  MostroMessage? _findMessageForStateUncached(
+      List<MostroMessage> messages, Status status) {
     // Filter out messages with invalid timestamps
     final validMessages =
         messages.where((m) => m.timestamp != null && m.timestamp! > 0).toList();

lib/services/nwc/nwc_client.dart

@@ -411,9 +411,14 @@ class NwcClient {
       // Only filter by kind + author; some NWC relay implementations
       // (e.g. Primal) don't support #e / #p tag filters, so we verify
       // the e-tag match in the event handler below.
+      // `since` bounds the replay: without it every request re-received the
+      // wallet's whole kind-23195 history from the relay (and the balance
+      // tick sends one request per minute). Responses are always newer than
+      // the request; one minute absorbs clock skew.
       final filter = NostrFilter(
         kinds: const [23195],
         authors: [connection.walletPubkey],
+        since: DateTime.now().subtract(const Duration(minutes: 1)),
       );
 
       final subId = 'nwc_${requestId.substring(0, 8)}';