fix(web): skip Remote Config realtime stream on web

The CachedRemoteConfigService constructor subscribed to
FirebaseRemoteConfig.onConfigUpdated with no onError handler. On web that
realtime stream cannot connect and emits `remoteconfig/stream-error`
continuously, so the errors escaped to runZonedGuarded and spammed SEVERE every
few seconds.

Skip the realtime subscription on web (config values still come from init's
bounded fetch and the cache), and add an onError handler so a transient stream
error no longer escapes to the zone on native either.

Author: SERDUN

lib/services/remote_config_service.dart

@@ -70,21 +70,30 @@ abstract class RemoteCacheConfigService {
 /// Implementation of [RemoteConfigService] using Firebase Remote Config.
 class CachedRemoteConfigService implements RemoteConfigService {
   CachedRemoteConfigService(this._cacheService, this._remoteConfig) {
-    _onConfigUpdatedSubscription = _remoteConfig.onConfigUpdated.listen((event) async {
-      _logger.info('Remote config update signal received. Updated keys: ${event.updatedKeys}');
-      try {
-        await _remoteConfig.activate();
-
-        // Guard against calling add/unawaited logic after the service is disposed.
-        if (_controller.isClosed) return;
-
-        final snapshot = _createSnapshot();
-        _controller.add(snapshot);
-        unawaited(_updateCache(snapshot));
-      } catch (e, stackTrace) {
-        _logger.warning('Failed to activate remote config update', e, stackTrace);
-      }
-    });
+    // Firebase Remote Config realtime updates are not available on web: the
+    // stream cannot connect and emits `remoteconfig/stream-error` continuously.
+    // Skip the subscription there - values still come from init's fetch and the
+    // cache. TODO(web): revisit if RC realtime ever works on web.
+    if (kIsWeb) return;
+    _onConfigUpdatedSubscription = _remoteConfig.onConfigUpdated.listen(
+      (event) async {
+        _logger.info('Remote config update signal received. Updated keys: ${event.updatedKeys}');
+        try {
+          await _remoteConfig.activate();
+
+          // Guard against calling add/unawaited logic after the service is disposed.
+          if (_controller.isClosed) return;
+
+          final snapshot = _createSnapshot();
+          _controller.add(snapshot);
+          unawaited(_updateCache(snapshot));
+        } catch (e, stackTrace) {
+          _logger.warning('Failed to activate remote config update', e, stackTrace);
+        }
+      },
+      // Without this, a transient realtime-stream error escapes to the zone.
+      onError: (Object e, StackTrace s) => _logger.warning('Remote config update stream error', e, s),
+    );
   }
 
   final FirebaseRemoteConfig _remoteConfig;