Refactor Chat API (#2804)

### What problem does this PR solve?

Refactor Chat API

### Type of change

- [x] Refactoring

---------

Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>

sdk/python/test/t_chat.py

@@ -0,0 +1,56 @@
+from ragflow import RAGFlow, Chat
+
+from common import API_KEY, HOST_ADDRESS
+from test_sdkbase import TestSdk
+
+
+class TestChat(TestSdk):
+    def test_create_chat_with_success(self):
+        """
+        Test creating an chat with success
+        """
+        rag = RAGFlow(API_KEY, HOST_ADDRESS)
+        kb = rag.create_dataset(name="test_create_chat")
+        chat = rag.create_chat("test_create", knowledgebases=[kb])
+        if isinstance(chat, Chat):
+            assert chat.name == "test_create", "Name does not match."
+        else:
+            assert False, f"Failed to create chat, error: {chat}"
+
+    def test_update_chat_with_success(self):
+        """
+        Test updating an chat with success.
+        """
+        rag = RAGFlow(API_KEY, HOST_ADDRESS)
+        kb = rag.create_dataset(name="test_update_chat")
+        chat = rag.create_chat("test_update", knowledgebases=[kb])
+        if isinstance(chat, Chat):
+            assert chat.name == "test_update", "Name does not match."
+            res=chat.update({"name":"new_chat"})
+            assert res is None, f"Failed to update chat, error: {res}"
+        else:
+            assert False, f"Failed to create chat, error: {chat}"
+
+    def test_delete_chats_with_success(self):
+        """
+        Test deleting an chat with success
+        """
+        rag = RAGFlow(API_KEY, HOST_ADDRESS)
+        kb = rag.create_dataset(name="test_delete_chat")
+        chat = rag.create_chat("test_delete", knowledgebases=[kb])
+        if isinstance(chat, Chat):
+            assert chat.name == "test_delete", "Name does not match."
+            res = rag.delete_chats(ids=[chat.id])
+            assert res is None, f"Failed to delete chat, error: {res}"
+        else:
+            assert False, f"Failed to create chat, error: {chat}"
+
+    def test_list_chats_with_success(self):
+        """
+        Test listing chats with success
+        """
+        rag = RAGFlow(API_KEY, HOST_ADDRESS)
+        list_chats = rag.list_chats()
+        assert len(list_chats) > 0, "Do not exist any chat"
+        for chat in list_chats:
+            assert isinstance(chat, Chat), "Existence type is not chat."