feature: show token usage in AI assistant result

Signed-off-by: leo <longshuang@msn.cn>

Author: love-linger

src/AI/Agent.cs

@@ -47,11 +47,15 @@ public async Task GenerateCommitMessageAsync(string repo, string changeList, Act
                 {
                     case ChatFinishReason.Stop:
                         onUpdate?.Invoke(string.Empty);
-                        onUpdate?.Invoke("[Assistant]:");
+                        onUpdate?.Invoke("# Assistant");
                         if (completion.Content.Count > 0)
                             onUpdate?.Invoke(completion.Content[0].Text);
                         else
                             onUpdate?.Invoke("[No content was generated.]");
+
+                        onUpdate?.Invoke(string.Empty);
+                        onUpdate?.Invoke("# Token Usage");
+                        onUpdate?.Invoke($"Total: {completion.Usage.TotalTokenCount}. Input: {completion.Usage.InputTokenCount}. Output: {completion.Usage.OutputTokenCount}");
                         break;
                     case ChatFinishReason.Length:
                         throw new Exception("The response was cut off because it reached the maximum length. Consider increasing the max tokens limit.");