### What problem does this PR solve?
- Implement RAGFlowWebApiAuth class for web API authentication
- Add comprehensive test cases for KB CRUD operations
- Set up common fixtures and utilities in conftest.py
- Add helper functions in common.py for web API requests
The changes establish a complete testing framework for knowledge base
management via web API endpoints.
### Type of change
- [x] Add test case
### 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
### What problem does this PR solve?
- Implement new SDK API test cases for chat assistant CRUD operations
- Enhance HTTP API concurrent tests to use as_completed for better
reliability
### Type of change
- [x] Add test cases
- [x] Refactoring
### What problem does this PR solve?
- Improve concurrent test cases by using as_completed for better
reliability
- Rename variables for clarity (chunk_num -> count)
- Add new SDK API test suite for chunk management operations
- Update HTTP API tests with consistent concurrency patterns
### Type of change
- [x] Add test cases
- [x] Refactoring
