whisper: Inference progress callback

[pminev]

Implement the inference progress callback for whisper.cpp integration used here in the library.

The callback works as notifier how much of the audio is being processed (encoded and decoded).

Progress is calculated by measuring the seeking in the audio.

1. Start at the beginning with variable seek 0
2. Call progress callback to the client with seek
3. Choose the best decoder - get it's seek_delta
4. Add seek_delta to seek
5. Back to 2) if the audio hasn't completed