feat: add partial completion sample and docs

Author: ikesnowy

README.zh-Hans.md

@@ -1049,6 +1049,86 @@ Usage: in(25)/out(7)/total(32)
  */
 ```
 
+### 前缀续写
+
+将需要续写的前缀作为 `assistant` 消息放到 `messages` 数组末尾，并将 `Partial` 设置为 `true`，大模型将根据这个前缀补全剩下的内容。
+
+这个模式下无法开启深度思考。
+
+示例请求
+
+```csharp
+var messages = new List<TextChatMessage>
+{
+    TextChatMessage.User("请补全这个 C# 函数，不要添加其他内容"),
+    TextChatMessage.Assistant("public int Fibonacci(int n)", partial: true)
+};
+
+var completion = client.GetTextCompletionStreamAsync(
+new ModelRequest<TextGenerationInput, ITextGenerationParameters>()
+{
+    Model = "qwen-turbo",
+    Input = new TextGenerationInput() { Messages = messages },
+    Parameters = new TextGenerationParameters()
+    {
+        ResultFormat = "message",
+        IncrementalOutput = true
+    }
+});
+```
+
+完整代码：
+
+```csharp
+var messages = new List<TextChatMessage>
+{
+    TextChatMessage.User("请补全这个 C# 函数，不要添加其他内容"),
+    TextChatMessage.Assistant("public int Fibonacci(int n)", partial: true)
+};
+Console.WriteLine($"User > {messages[0].Content}");
+Console.Write($"Assistant > {messages[1].Content}");
+var completion = client.GetTextCompletionStreamAsync(
+    new ModelRequest<TextGenerationInput, ITextGenerationParameters>()
+    {
+        Model = "qwen-turbo",
+        Input = new TextGenerationInput() { Messages = messages },
+        Parameters = new TextGenerationParameters()
+        {
+            ResultFormat = "message",
+            IncrementalOutput = true
+        }
+    });
+var reply = new StringBuilder();
+TextGenerationTokenUsage? usage = null;
+await foreach (var chunk in completion)
+{
+    var choice = chunk.Output.Choices![0];
+    Console.Write(choice.Message.Content);
+    reply.Append(choice.Message.Content);
+    usage = chunk.Usage;
+}
+
+Console.WriteLine();
+messages.Add(TextChatMessage.Assistant(reply.ToString()));
+if (usage != null)
+{
+    Console.WriteLine(
+        $"Usage: in({usage.InputTokens})/out({usage.OutputTokens})/reasoning({usage.OutputTokensDetails?.ReasoningTokens})/total({usage.TotalTokens})");
+}
+
+/*
+User > 请补全这个 C# 函数，不要添加其他内容
+Assistant > public int Fibonacci(int n)
+{
+    if (n <= 1)
+        return n;
+
+    return Fibonacci(n - 1) + Fibonacci(n - 2);
+}
+Usage: in(31)/out(34)/reasoning()/total(65)
+ */
+```
+
 
 
 ### 多模态

sample/Cnblogs.DashScope.Sample/Text/PrefixCompletionSample.cs

@@ -0,0 +1,58 @@
+using System.Text;
+using Cnblogs.DashScope.Core;
+
+namespace Cnblogs.DashScope.Sample.Text;
+
+public class PrefixCompletionSample : ISample
+{
+    /// <inheritdoc />
+    public string Description => "Prefix completion sample";
+
+    /// <inheritdoc />
+    public async Task RunAsync(IDashScopeClient client)
+    {
+        var messages = new List<TextChatMessage>
+        {
+            TextChatMessage.User("请补全这个 C# 函数，不要添加其他内容"),
+            TextChatMessage.Assistant("public int Fibonacci(int n)", partial: true)
+        };
+        Console.WriteLine($"User > {messages[0].Content}");
+        Console.Write($"Assistant > {messages[1].Content}");
+        var completion = client.GetTextCompletionStreamAsync(
+            new ModelRequest<TextGenerationInput, ITextGenerationParameters>()
+            {
+                Model = "qwen-turbo",
+                Input = new TextGenerationInput() { Messages = messages },
+                Parameters = new TextGenerationParameters() { ResultFormat = "message", IncrementalOutput = true }
+            });
+        var reply = new StringBuilder();
+        TextGenerationTokenUsage? usage = null;
+        await foreach (var chunk in completion)
+        {
+            var choice = chunk.Output.Choices![0];
+            Console.Write(choice.Message.Content);
+            reply.Append(choice.Message.Content);
+            usage = chunk.Usage;
+        }
+
+        Console.WriteLine();
+        messages.Add(TextChatMessage.Assistant(reply.ToString()));
+        if (usage != null)
+        {
+            Console.WriteLine(
+                $"Usage: in({usage.InputTokens})/out({usage.OutputTokens})/reasoning({usage.OutputTokensDetails?.ReasoningTokens})/total({usage.TotalTokens})");
+        }
+    }
+}
+
+/*
+User > 请补全这个 C# 函数，不要添加其他内容
+Assistant > public int Fibonacci(int n)
+{
+    if (n <= 1)
+        return n;
+
+    return Fibonacci(n - 1) + Fibonacci(n - 2);
+}
+Usage: in(31)/out(34)/reasoning()/total(65)
+ */