Merge and refactor live audio commit from gencerege/vad

[mattieerolainnofactorcom]

I'm using this code with Google Gemini Live API for client side VAD . Code in #191 was so many commits behind current master branch that I had problems just merging it. I instead refactored it and wrote some unit tests to verify that the changes don't break old functionality.

Here is how I use the events with @google/genai Session:

            onSpeechRealStart: () => {
                session.sendRealtimeInput({ activityStart: {} })
            },
            onEmitChunk: (audio) => {
                session.sendRealtimeInput({
                    audio: this.createBlob(audio)
                });
            },
            onSpeechEnd: (audio) => {
                session.sendRealtimeInput({
                    audio: this.createBlob(audio)
                });

                session.sendRealtimeInput({ activityEnd: {} })
            }

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