feat(channel): add getChannelHistoryMessages binding

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

android/src/main/java/io/openim/flutter_openim_sdk/manager/ChannelManager.java

@@ -100,4 +100,14 @@ public class ChannelManager extends BaseManager {
                 jsonValue(methodCall, "userIDs")
         );
     }
+
+    public void getChannelHistoryMessages(MethodCall methodCall, MethodChannel.Result result) {
+        Open_im_sdk.getChannelHistoryMessages(
+                new OnBaseListener(result, methodCall),
+                value(methodCall, "operationID"),
+                value(methodCall, "channelID"),
+                value(methodCall, "count"),
+                int2long(methodCall, "sinceSeq")
+        );
+    }
 }

ios/Classes/Module/ChannelManager.swift

@@ -17,6 +17,7 @@ public class ChannelManager: BaseServiceManager {
 
 
         self["getUsersInChannel"] = getUsersInChannel
+        self["getChannelHistoryMessages"] = getChannelHistoryMessages
         self["isJoinChannel"] = isJoinChannel
         self["joinChannel"] = joinChannel
         self["quitChannel"] = quitChannel
@@ -50,6 +51,10 @@ public class ChannelManager: BaseServiceManager {
          methodCall[jsonString: "userIDs"])
     }
 
+    func getChannelHistoryMessages(methodCall: FlutterMethodCall, result: @escaping FlutterResult) {
+        Open_im_sdkGetChannelHistoryMessages(BaseCallback(result: result), methodCall[string: "operationID"], methodCall[string: "channelID"], methodCall[int: "count"], methodCall[int64: "sinceSeq"])
+    }
+
     func isJoinChannel(methodCall: FlutterMethodCall, result: @escaping FlutterResult) {
         Open_im_sdkIsJoinChannel(BaseCallback(result: result), methodCall[string: "operationID"], methodCall[string: "channelID"])
     }

lib/src/manager/im_channel_manager.dart

@@ -309,6 +309,25 @@ class ChannelManager {
             'operationID': Utils.checkOperationID(operationID),
           }));
 
+  /// Get channel short-term history messages
+  /// [channelID] Channel ID
+  /// [count] Number of messages to retrieve
+  /// [sinceSeq] Internal sequence cursor for pagination (0 for first page)
+  Future<dynamic> getChannelHistoryMessages({
+    required String channelID,
+    int count = 20,
+    int sinceSeq = 0,
+    String? operationID,
+  }) =>
+      _channel.invokeMethod(
+          'getChannelHistoryMessages',
+          _buildParam({
+            'channelID': channelID,
+            'count': count,
+            'sinceSeq': sinceSeq,
+            'operationID': Utils.checkOperationID(operationID),
+          }));
+
   static Map _buildParam(Map<String, dynamic> param) {
     param["ManagerName"] = "channelManager";
     param = Utils.cleanMap(param);