## Summary
Relate to #17284
Migrate four OpenAI-compatible drivers (`nvidia`, `siliconflow`, `groq`,
`longcat`) to use the unified response handlers
(`HandleNonStreamingResponse` / `HandleStreamingResponse`), following
the same pattern established by `deepseek` in #17634.
- Cut ~100 lines per driver (541 lines removed, 19 added across 4
files).
- `nvidia` now extracts token usage (previously had none).
- All four drivers produce the unified `StreamUsage` log.