refactor: clean up deprecated APIs for v6.1.0 (#521)

## Changes
- Renamed `getAvailablePurchases()` to `getActivePurchases()` for
clarity
- Renamed `getPurchaseHistory()` to `getPurchaseHistories()` for
consistency
- Removed all deprecated methods marked for removal in v6.0.0
- Cleaned up legacy code and unused methods
- Updated example code to use new APIs

## Breaking Changes
- `getAvailablePurchases()` → `getActivePurchases()`
- Removed deprecated methods: `initialize()`, `checkSubscribed()`,
`getAvailablePurchasesAsync()`, etc.

## Migration Guide
- Replace `getAvailablePurchases()` with `getActivePurchases()`
- Replace `getPurchaseHistory()` with `getPurchaseHistories()`
- Use `initConnection()` instead of `initialize()`
- Use `finishTransaction()` instead of deprecated platform-specific
methods

Author: hyochan

example/ios/Flutter/Flutter.podspec

@@ -0,0 +1,18 @@
+#
+# This podspec is NOT to be published. It is only used as a local source!
+# This is a generated file; do not edit or check into version control.
+#
+
+Pod::Spec.new do |s|
+  s.name             = 'Flutter'
+  s.version          = '1.0.0'
+  s.summary          = 'A UI toolkit for beautiful and fast apps.'
+  s.homepage         = 'https://flutter.dev'
+  s.license          = { :type => 'BSD' }
+  s.author           = { 'Flutter Dev Team' => '[email protected]' }
+  s.source           = { :git => 'https://github.com/flutter/engine', :tag => s.version.to_s }
+  s.ios.deployment_target = '13.0'
+  # Framework linking is handled by Flutter tooling, not CocoaPods.
+  # Add a placeholder to satisfy `s.dependency 'Flutter'` plugin podspecs.
+  s.vendored_frameworks = 'path/to/nothing'
+end

example/lib/src/screens/available_purchases_screen.dart

@@ -1,5 +1,4 @@
 import 'dart:async';
-import 'dart:io' show Platform;
 import 'package:flutter/material.dart';
 import 'package:flutter/cupertino.dart';
 import 'package:flutter_inapp_purchase/flutter_inapp_purchase.dart';
@@ -16,7 +15,7 @@ class _AvailablePurchasesScreenState extends State<AvailablePurchasesScreen> {
   final FlutterInappPurchase _iap = FlutterInappPurchase.instance;
 
   List<Purchase> _availablePurchases = [];
-  List<PurchasedItem> _purchaseHistory = [];
+  List<Purchase> _purchaseHistory = [];
   bool _loading = false;
   bool _connected = false;
   String? _error;
@@ -67,14 +66,14 @@ class _AvailablePurchasesScreenState extends State<AvailablePurchasesScreen> {
 
     try {
       // Load available purchases (non-consumed)
-      final availablePurchases = await _iap.getAvailablePurchases();
+      final availablePurchases = await _iap.getActivePurchases();
 
       // Load purchase history
-      final purchaseHistory = await _iap.getPurchaseHistory();
+      final purchaseHistory = await _iap.getPurchaseHistories();
 
       setState(() {
         _availablePurchases = availablePurchases;
-        _purchaseHistory = purchaseHistory ?? [];
+        _purchaseHistory = purchaseHistory;
       });
     } catch (e) {
       setState(() {
@@ -95,7 +94,7 @@ class _AvailablePurchasesScreenState extends State<AvailablePurchasesScreen> {
     });
 
     try {
-      final restored = await _iap.getAvailablePurchases();
+      final restored = await _iap.getActivePurchases();
       setState(() {
         _availablePurchases = restored;
       });
@@ -208,7 +207,7 @@ class _AvailablePurchasesScreenState extends State<AvailablePurchasesScreen> {
     );
   }
 
-  Widget _buildPurchaseHistoryItem(PurchasedItem item) {
+  Widget _buildPurchaseHistoryItem(Purchase item) {
     return Card(
       margin: const EdgeInsets.only(bottom: 8),
       child: Padding(
@@ -221,7 +220,7 @@ class _AvailablePurchasesScreenState extends State<AvailablePurchasesScreen> {
               children: [
                 Expanded(
                   child: Text(
-                    item.productId ?? 'Unknown Product',
+                    item.productId.isEmpty ? 'Unknown Product' : item.productId,
                     style: const TextStyle(
                       fontSize: 16,
                       fontWeight: FontWeight.w600,

example/lib/src/screens/debug_purchases_screen.dart

@@ -36,7 +36,7 @@ class _DebugPurchasesScreenState extends State<DebugPurchasesScreen> {
       await Future<void>.delayed(const Duration(seconds: 1));
 
       // Get all available purchases
-      final purchases = await _iap.getAvailablePurchases();
+      final purchases = await _iap.getActivePurchases();
 
       setState(() {
         _purchases = purchases;

example/lib/src/screens/subscription_flow_screen.dart

@@ -26,8 +26,6 @@ class _SubscriptionFlowScreenState extends State<SubscriptionFlowScreen> {
   bool _isConnecting = true;
   bool _isLoadingProducts = false;
   String? _purchaseResult;
-  String? _initError;
-  Purchase? _currentPurchase;
   StreamSubscription<Purchase>? _purchaseUpdatedSubscription;
   StreamSubscription<PurchaseError>? _purchaseErrorSubscription;
 
@@ -58,9 +56,7 @@ class _SubscriptionFlowScreenState extends State<SubscriptionFlowScreen> {
       });
 
       if (!_connected) {
-        setState(() {
-          _initError = 'Failed to connect to store';
-        });
+        debugPrint('Failed to connect to store');
         return;
       }
 
@@ -102,7 +98,7 @@ class _SubscriptionFlowScreenState extends State<SubscriptionFlowScreen> {
         debugPrint('TransactionId: ${purchase.transactionId}');
         _handlePurchaseUpdate(purchase);
       },
-      onError: (error) {
+      onError: (Object error) {
         debugPrint('❌ Subscription stream error: $error');
       },
     );
@@ -125,7 +121,6 @@ class _SubscriptionFlowScreenState extends State<SubscriptionFlowScreen> {
 
     setState(() {
       _isProcessing = false;
-      _currentPurchase = purchase;
 
       // Format subscription result like KMP-IAP
       _purchaseResult = '''
@@ -195,7 +190,7 @@ Platform: ${error.platform}
 
   Future<void> _loadActiveSubscriptions() async {
     try {
-      final purchases = await _iap.getAvailablePurchases();
+      final purchases = await _iap.getActivePurchases();
       setState(() {
         _activeSubscriptions = purchases
             .where((p) => subscriptionIds.contains(p.productId))
@@ -503,7 +498,6 @@ Platform: ${error.platform}
                           onPressed: () {
                             setState(() {
                               _purchaseResult = null;
-                              _currentPurchase = null;
                             });
                           },
                         ),