examples : update vad support in stream example

[danbev]

This commit updates the stream example to use the VAD support in whisper instead of the simple_vad that it currently uses.

wip

[mdestagnol]

Following up on my comment on another PR. Just a few thoughts as I was reading your great work on VAD.

Currently, VAD is used in the stream example as a way to only send to whisper the samples containing voice. This is an optimization in terms of compute but I wonder if we miss on the benefits of accuracy.

Similarly to how we have a sliding window when not using VAD in this stream example, we could leverage VAD to attempt to chunk the audio during silence rather than in the middle of a word– sort of a dynamic sliding window.

We could also keep a part of the previous sample, similar to what we do when not using VAD. That would allow better accuracy in case there's no good silence where to chunk.

Finally, is there a reason why we don't reinject the previous tokens in the prompt when using VAD? -> nevermind this is already implemented in your PR :)