Add large file upload enhancements and tests (#43)
- Add upload duration/throughput metrics (duration_ms, throughput_mbps) to response
- Add upload progress logging for large files (hash computation and multipart upload)
- Add client disconnect handling during uploads with proper cleanup
- Add upload progress tracking endpoint GET /upload/{upload_id}/progress
- Add large file upload tests (10MB, 100MB, 1GB)
- Add upload cancellation and timeout handling tests
- Add API documentation for upload endpoints with curl, Python, JavaScript examples
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