Fix hardware realtime downscaling lag

[DjDeveloperr]

Summary

• Prefer the software scaler for realtime hardware/auto downscales when the source format supports it, avoiding the slower VideoToolbox transfer path in the hot loop.
• Let hardware pacing respond to realtime encode latency instead of only the software low-latency mode.
• Loosen the hardware interval floor so backoff can settle further when the encoder falls behind.

Testing

• npm run build:cli passed and rebuilt the native CLI successfully.
• No browser/UI test run was needed for this native encoder change.