Add optional KYC flow and service-backed account limits

frontend/packages/sxchnge_kyc/lib/src/models/limits.dart

@@ -0,0 +1,31 @@
+enum AccountTier { basic, verified }
+
+enum LimitPeriod { day, month }
+
+class VisibleLimit {
+  const VisibleLimit({
+    required this.period,
+    required this.currency,
+    required this.basicMinor,
+    required this.verifiedMinor,
+    required this.currentMinor,
+    required this.remainingMinor,
+  });
+  final LimitPeriod period;
+  final String currency;
+  final int basicMinor;
+  final int verifiedMinor;
+  final int currentMinor;
+  final int remainingMinor;
+}
+
+class Limits {
+  Limits({
+    required this.tier,
+    required List<VisibleLimit> rows,
+    required this.simulated,
+  }) : rows = List.unmodifiable(rows);
+  final AccountTier tier;
+  final List<VisibleLimit> rows;
+  final bool simulated;
+}