feat：统一replyer在是否多模态下的表现，提高一致性和通用性，新增模型visual参数

pytests/test_prompt_message_roundtrip.py

@@ -0,0 +1,18 @@
+from src.llm_models.payload_content.message import MessageBuilder, RoleType
+from src.plugin_runtime.hook_payloads import deserialize_prompt_messages, serialize_prompt_messages
+
+
+def test_prompt_messages_roundtrip_preserves_image_parts() -> None:
+    messages = [
+        MessageBuilder().set_role(RoleType.User).add_text_content("你好").add_image_content("png", "ZmFrZQ==").build(),
+    ]
+
+    serialized_messages = serialize_prompt_messages(messages)
+    restored_messages = deserialize_prompt_messages(serialized_messages)
+
+    assert len(restored_messages) == 1
+    assert restored_messages[0].role == RoleType.User
+    assert restored_messages[0].get_text_content() == "你好"
+    assert len(restored_messages[0].parts) == 2
+    assert restored_messages[0].parts[1].image_format == "png"
+    assert restored_messages[0].parts[1].image_base64 == "ZmFrZQ=="