add encode method for model list

MVMCore/MVMCore/Models/Model/ModelRegistry.swift

@@ -125,4 +125,12 @@ extension KeyedEncodingContainer where Key: CodingKey {
         let encoder = self.superEncoder(forKey: key)
         try value.encode(to: encoder)
     }
+    
+    ///need instance type as input paramaeter list
+    public mutating func encodeArray<T:Model>(_ list:[T]?, forKey key:KeyedEncodingContainer<K>.Key) throws {
+        var unkeyedContainer = self.nestedUnkeyedContainer(forKey: key)
+        try list?.forEach({ (model) in
+            try unkeyedContainer.encode(model)
+        })
+    }
 }