feat(llc): add contains and empty filters

packages/stream_chat/lib/src/core/models/filter.dart

@@ -51,6 +51,9 @@ enum FilterOperator {
 
   /// Matches none of the values specified in an array.
   nor,
+
+  /// Matches any list that contains the specified values
+  contains,
 }
 
 /// Helper extension for [FilterOperator]
@@ -71,6 +74,7 @@ extension FilterOperatorX on FilterOperator {
         FilterOperator.and: '\$and',
         FilterOperator.or: '\$or',
         FilterOperator.nor: '\$nor',
+        FilterOperator.contains: '\$contains',
       }[this]!;
 }
 
@@ -157,6 +161,10 @@ class Filter extends Equatable {
   factory Filter.exists(String key, {bool exists = true}) =>
       Filter._(operator: FilterOperator.exists, key: key, value: exists);
 
+  /// Matches any list that contains the specified values
+  factory Filter.contains(String key, List<Object> values) =>
+      Filter._(operator: FilterOperator.contains, key: key, value: values);
+
   /// Creates a custom [Filter] if there isn't one already available.
   const factory Filter.custom({
     required Object value,
@@ -164,6 +172,9 @@ class Filter extends Equatable {
     String? key,
   }) = Filter.__;
 
+  /// An empty filter
+  factory Filter.empty() => const Filter.raw(value: {});
+
   /// Creates a custom [Filter] from a raw map value
   ///
   /// ```dart