feat: add support for broadcast replay configuration (#1242)

* feat: add support for broadcast replay configuration

Added ReplayOption class and replay field to RealtimeChannelConfig
to support configuring broadcast replay with 'since' timestamp and optional
'limit' parameter. Broadcast callbacks will automatically receive meta field
with replayed status and message id when replay is enabled.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

* docs: improve docs for broadcast replay

---------

Co-authored-by: Claude <[email protected]>

Author: grdsdev

packages/realtime_client/lib/src/types.dart

@@ -138,13 +138,39 @@ extension ToType on RealtimeListenTypes {
   }
 }
 
+/// Configuration for broadcast replay feature.
+/// Allows replaying broadcast messages from a specific timestamp.
+class ReplayOption {
+  /// Unix timestamp (in milliseconds) from which to start replaying messages
+  final int since;
+
+  /// Optional limit on the number of messages to replay, maximum value of 25.
+  final int? limit;
+
+  const ReplayOption({
+    required this.since,
+    this.limit,
+  });
+
+  Map<String, dynamic> toMap() {
+    final map = <String, dynamic>{'since': since};
+    if (limit != null) {
+      map['limit'] = limit;
+    }
+    return map;
+  }
+}
+
 class RealtimeChannelConfig {
   /// [ack] option instructs server to acknowlege that broadcast message was received
   final bool ack;
 
   /// [self] option enables client to receive message it broadcasted
   final bool self;
 
+  /// [replay] enables **private** channels to access messages that were sent earlier. Only messages published via [Broadcast From the Database](https://supabase.com/docs/guides/realtime/broadcast#trigger-broadcast-messages-from-your-database) are available for replay.
+  final ReplayOption? replay;
+
   /// [key] option is used to track presence payload across clients
   final String key;
 
@@ -157,18 +183,24 @@ class RealtimeChannelConfig {
   const RealtimeChannelConfig({
     this.ack = false,
     this.self = false,
+    this.replay,
     this.key = '',
     this.enabled = false,
     this.private = false,
   });
 
   Map<String, dynamic> toMap() {
+    final broadcastConfig = <String, dynamic>{
+      'ack': ack,
+      'self': self,
+    };
+    if (replay != null) {
+      broadcastConfig['replay'] = replay!.toMap();
+    }
+
     return {
       'config': {
-        'broadcast': {
-          'ack': ack,
-          'self': self,
-        },
+        'broadcast': broadcastConfig,
         'presence': {
           'key': key,
           'enabled': enabled,