Add a "total" field to All List APIs (HTTP & Python SDK)

[kswen]

What problem does this PR solve?

Add a "total" field to all List APIs (HTTP & Python SDK) to resolve pagination inaccuracies when integrating with third-party systems.

1. HTTP API

All list endpoints (datasets, documents, chunks, chat assistants, agent sessions, chat sessions) now return a response with the following top-level fields:

• total: Total number of items matching the query.
• page: Current page number.
• page_size: Number of items per page.
• The list of objects (e.g., datasets, docs, chunks, chats, agents, sessions).
• Backend service layer updated to ensure correct calculation of total before pagination is applied.

2. Python SDK Updates

All list_* methods in the SDK (e.g., list_datasets, list_documents, list_chunks, list_chats, list_agents, list_sessions) now return a dictionary with:

• total, page, page_size, and the relevant list.
• All relevant SDK modules (ragflow.py, modules/dataset.py, modules/document.py, modules/chat.py, modules/agent.py) updated to match the new API structure.

3. Test Suite Updates

• HTTP API tests: All tests for list endpoints now assert the presence and type of total, page, and page_size in the response, and check the list length via the new structure.
• Python SDK tests: All SDK tests for list methods updated to check for the new dict structure and validate the types of the new fields.

4. Documentation Updates

HTTP API Reference: All relevant list endpoint sections updated to show the new response structure, including example JSON responses and field descriptions.

Python API Reference:

• Migration note added at the top, explaining the new return structure for all list methods.
• All method signatures, return value descriptions, and code examples updated to show the new dict structure.
• Example code blocks now demonstrate how to access the list and pagination fields.
• Minor corrections and improvements to code examples and parameter descriptions for clarity and accuracy.

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

[yingfeng]

Thanks, please make sure to pass API test in CI

[kswen]

@yingfeng Hey, the failed test cases have been updated; please give it another CI shot, thanks!

[kswen]

All relevant test cases have been updated again.
waiting for give it another ci shot

[kswen]

@yingfeng
If resources are available, please run another CI build. I can fix any remaining issues ASAP