Usage logging V2: grouped JSON schema, endpoint tracking, GPU profiling

Remove dead code and add GPU VRAM profiling

Prevent CUDA state poisoning and add thread-safe GPU lifecycle management

Compress logging audio format

Fix race condition where concurrent quota exhaustion permanently breaks GPU

Widen DP lookback window and fix null-typed parquet columns

Fix delay between progress bar completion and results displaying

Restructure src/ for cleaner modularity