Allow saving filters

example/lib/data/saved_scan_filter.dart

@@ -0,0 +1,63 @@
+import 'dart:convert';
+
+/// A saved scan filter preset (name + the three filter field values).
+class SavedScanFilter {
+  const SavedScanFilter({
+    required this.name,
+    required this.services,
+    required this.namePrefix,
+    required this.manufacturerData,
+  });
+
+  final String name;
+  final String services;
+  final String namePrefix;
+  final String manufacturerData;
+
+  Map<String, dynamic> toJson() => {
+        'name': name,
+        'services': services,
+        'namePrefix': namePrefix,
+        'manufacturerData': manufacturerData,
+      };
+
+  factory SavedScanFilter.fromJson(Map<String, dynamic> json) {
+    return SavedScanFilter(
+      name: json['name'] as String? ?? '',
+      services: json['services'] as String? ?? '',
+      namePrefix: json['namePrefix'] as String? ?? '',
+      manufacturerData: json['manufacturerData'] as String? ?? '',
+    );
+  }
+
+  static List<SavedScanFilter> fromJsonList(String? jsonString) {
+    if (jsonString == null || jsonString.isEmpty) return [];
+    try {
+      final list = jsonDecode(jsonString) as List<dynamic>?;
+      if (list == null) return [];
+      return list
+          .map((e) => SavedScanFilter.fromJson(e as Map<String, dynamic>))
+          .toList();
+    } catch (_) {
+      return [];
+    }
+  }
+
+  static String toJsonList(List<SavedScanFilter> filters) {
+    return jsonEncode(filters.map((e) => e.toJson()).toList());
+  }
+
+  SavedScanFilter copyWith({
+    String? name,
+    String? services,
+    String? namePrefix,
+    String? manufacturerData,
+  }) {
+    return SavedScanFilter(
+      name: name ?? this.name,
+      services: services ?? this.services,
+      namePrefix: namePrefix ?? this.namePrefix,
+      manufacturerData: manufacturerData ?? this.manufacturerData,
+    );
+  }
+}