fix: Adds support for SharedPreferencesAsync

packages/supabase_flutter/lib/src/local_storage.dart

@@ -64,19 +64,32 @@ class EmptyLocalStorage extends LocalStorage {
 /// A [LocalStorage] implementation that implements SharedPreferences as the
 /// storage method.
 class SharedPreferencesLocalStorage extends LocalStorage {
-  late final SharedPreferences _prefs;
+  late final SharedPreferences _syncPrefs;
+
+  late final SharedPreferencesAsync _asyncPrefs;
 
-  SharedPreferencesLocalStorage({required this.persistSessionKey});
+  SharedPreferencesLocalStorage({
+    required this.persistSessionKey,
+    this.useSharedPreferencesAsync = false,
+  });
 
   final String persistSessionKey;
+
+  final bool useSharedPreferencesAsync;
+
   static const _useWebLocalStorage =
       kIsWeb && bool.fromEnvironment("dart.library.js_interop");
 
   @override
   Future<void> initialize() async {
     if (!_useWebLocalStorage) {
       WidgetsFlutterBinding.ensureInitialized();
-      _prefs = await SharedPreferences.getInstance();
+
+      if (useSharedPreferencesAsync) {
+        _asyncPrefs = SharedPreferencesAsync();
+      } else {
+        _syncPrefs = await SharedPreferences.getInstance();
+      }
     }
   }
 
@@ -85,23 +98,36 @@ class SharedPreferencesLocalStorage extends LocalStorage {
     if (_useWebLocalStorage) {
       return web.hasAccessToken(persistSessionKey);
     }
-    return _prefs.containsKey(persistSessionKey);
+
+    return switch (useSharedPreferencesAsync) {
+      true => _asyncPrefs.containsKey(persistSessionKey),
+      false => Future.value(_syncPrefs.containsKey(persistSessionKey)),
+    };
   }
 
   @override
   Future<String?> accessToken() async {
     if (_useWebLocalStorage) {
       return web.accessToken(persistSessionKey);
     }
-    return _prefs.getString(persistSessionKey);
+
+    return switch (useSharedPreferencesAsync) {
+      true => _asyncPrefs.getString(persistSessionKey),
+      false => Future.value(_syncPrefs.getString(persistSessionKey)),
+    };
   }
 
   @override
   Future<void> removePersistedSession() async {
     if (_useWebLocalStorage) {
       web.removePersistedSession(persistSessionKey);
     } else {
-      await _prefs.remove(persistSessionKey);
+      switch (useSharedPreferencesAsync) {
+        case true:
+          await _asyncPrefs.remove(persistSessionKey);
+        case false:
+          await _syncPrefs.remove(persistSessionKey);
+      }
     }
   }
 
@@ -110,7 +136,10 @@ class SharedPreferencesLocalStorage extends LocalStorage {
     if (_useWebLocalStorage) {
       return web.persistSession(persistSessionKey, persistSessionString);
     }
-    return _prefs.setString(persistSessionKey, persistSessionString);
+    return switch (useSharedPreferencesAsync) {
+      true => _asyncPrefs.setString(persistSessionKey, persistSessionString),
+      false => _syncPrefs.setString(persistSessionKey, persistSessionString),
+    };
   }
 }