fix: keep getter in constants class

Author: Vinzent03

packages/supabase/lib/src/constants.dart

@@ -1,7 +1,11 @@
 import 'package:supabase/src/version.dart';
-import 'platform_stub.dart' if (dart.library.io) 'platform_io.dart';
+import 'platform_stub.dart' if (dart.library.io) 'platform_io.dart'
+    as cond_platform;
 
 class Constants {
+  static String? get platform => cond_platform.platform;
+  static String? get platformVersion => cond_platform.platformVersion;
+
   static final Map<String, String> defaultHeaders = {
     'X-Client-Info': 'supabase-dart/$version',
     if (platform != null)

packages/supabase/test/utilities_test.dart

@@ -9,6 +9,8 @@ import 'package:supabase/src/counter.dart';
 import 'package:supabase/src/supabase_event_types.dart';
 import 'package:test/test.dart';
 
+const bool kIsWeb = bool.fromEnvironment('dart.library.js_util');
+
 void main() {
   group('Counter', () {
     late Counter counter;