feat: support feishu code block

nanobot/channels/feishu.py

@@ -191,6 +191,10 @@ def _extract_post_content(content_json: dict) -> tuple[str, list[str]]:
                     texts.append(el.get("text", ""))
                 elif tag == "at":
                     texts.append(f"@{el.get('user_name', 'user')}")
+                elif tag == "code_block":
+                    lang = el.get("language", "")
+                    code_text = el.get("text", "")
+                    texts.append(f"\n```{lang}\n{code_text}\n```\n")
                 elif tag == "img" and (key := el.get("image_key")):
                     images.append(key)
         return (" ".join(texts).strip() or None), images