Integrate secure storage service

finlog_app/fluttery/lib/src/storage/secure/secure_storage_impl.dart

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+import 'package:flutter/material.dart';
+import 'package:flutter_secure_storage/flutter_secure_storage.dart';
+import 'package:fluttery/secure_storage.dart';
+
+class SecureStorageImpl implements SecureStorage {
+  final FlutterSecureStorage _secureStorage;
+
+  /// Constructor - creates a single instance with default FlutterSecureStorage
+  SecureStorageImpl() : _secureStorage = const FlutterSecureStorage();
+
+  /// Testing constructor
+  @visibleForTesting
+  SecureStorageImpl.forTesting({required FlutterSecureStorage instance})
+    : _secureStorage = instance;
+
+  @override
+  Future<void> write(String key, String value) async {
+    await _secureStorage.write(key: key, value: value);
+  }
+
+  @override
+  Future<String?> read(String key) async {
+    return await _secureStorage.read(key: key);
+  }
+
+  @override
+  Future<bool> containsKey(String key) async {
+    return await _secureStorage.containsKey(key: key);
+  }
+
+  @override
+  Future<void> delete(String key) async {
+    await _secureStorage.delete(key: key);
+  }
+
+  @override
+  Future<void> deleteAll() async {
+    await _secureStorage.deleteAll();
+  }
+
+  @override
+  Future<Set<String>> readAll() async {
+    final allData = await _secureStorage.readAll();
+    return allData.keys.toSet();
+  }
+
+  @override
+  Future<Set<String>> readAllKeys() async {
+    final allData = await _secureStorage.readAll();
+    return allData.keys.toSet();
+  }
+
+  @override
+  Future<void> writeInt(String key, int value) async {
+    await _secureStorage.write(key: key, value: value.toString());
+  }
+
+  @override
+  Future<int?> readInt(String key) async {
+    final value = await _secureStorage.read(key: key);
+    if (value == null) return null;
+    return int.tryParse(value);
+  }
+
+  @override
+  Future<void> writeBool(String key, bool value) async {
+    await _secureStorage.write(key: key, value: value.toString());
+  }
+
+  @override
+  Future<bool?> readBool(String key) async {
+    final value = await _secureStorage.read(key: key);
+    if (value == null) return null;
+    if (value.toLowerCase() == 'true') return true;
+    if (value.toLowerCase() == 'false') return false;
+    return null; // Invalid boolean value
+  }
+
+  @override
+  Future<void> writeDouble(String key, double value) async {
+    await _secureStorage.write(key: key, value: value.toString());
+  }
+
+  @override
+  Future<double?> readDouble(String key) async {
+    final value = await _secureStorage.read(key: key);
+    if (value == null) return null;
+    return double.tryParse(value);
+  }
+}