### 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
### What problem does this PR solve?
- Removed hardcoded Zhipu API key from codebase
- New requirement: Tests now require ZHIPU_AI_API_KEY environment
variable
Example: export ZHIPU_AI_API_KEY=your_api_key_here
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)