Test: Refactor test fixtures and add SDK session management tests (#8141)

### What problem does this PR solve?

- Consolidate HTTP API test fixtures using batch operations
(batch_add_chunks, batch_create_chat_assistants)
- Fix fixture initialization order in clear_session_with_chat_assistants
- Add new SDK API test suite for session management
(create/delete/list/update)

### Type of change

- [x] Add test cases
- [x] Refactoring

test/testcases/test_sdk_api/test_session_management/conftest.py

@@ -0,0 +1,49 @@
+#
+#  Copyright 2025 The InfiniFlow Authors. All Rights Reserved.
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+#
+import pytest
+from common import batch_add_sessions_with_chat_assistant
+from pytest import FixtureRequest
+from ragflow_sdk import Chat, DataSet, Document, Session
+
+
+@pytest.fixture(scope="class")
+def add_sessions_with_chat_assistant(request: FixtureRequest, add_chat_assistants: tuple[DataSet, Document, list[Chat]]) -> tuple[Chat, list[Session]]:
+    def cleanup():
+        for chat_assistant in chat_assistants:
+            try:
+                chat_assistant.delete_sessions(ids=None)
+            except Exception:
+                pass
+
+    request.addfinalizer(cleanup)
+
+    _, _, chat_assistants = add_chat_assistants
+    return chat_assistants[0], batch_add_sessions_with_chat_assistant(chat_assistants[0], 5)
+
+
+@pytest.fixture(scope="function")
+def add_sessions_with_chat_assistant_func(request: FixtureRequest, add_chat_assistants: tuple[DataSet, Document, list[Chat]]) -> tuple[Chat, list[Session]]:
+    def cleanup():
+        for chat_assistant in chat_assistants:
+            try:
+                chat_assistant.delete_sessions(ids=None)
+            except Exception:
+                pass
+
+    request.addfinalizer(cleanup)
+
+    _, _, chat_assistants = add_chat_assistants
+    return chat_assistants[0], batch_add_sessions_with_chat_assistant(chat_assistants[0], 5)