### 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