feat: voice-activity streaming mode & inner-vad for speech-to-text module

[IgorSwat]

Description

This PR introduces changes focused on voice-activity-detection module and it's utilization within the library:

• Native side VAD streaming - introduces a continuous voice-activity-detection mechanism with user-friendly callback system. Example usage from demo app:

  await model.stream({
    onSpeechBegin: () => {...},
    onSpeechEnd: () => {...},
    options: {...},
  });

• VAD x STT integration - adds an option to utilize voice-activity-detection within the speech-to-text module, significantly improving the effective performance of the STT.
• Demo apps: introduces new screen in the speech demo app: VoiceActivityDetectionScreen and changes the behavior of SpeechToTextScreen, adding a toggle to switch the VAD submodule for STT on/off.

Introduces a breaking change?

• Yes
• No

Type of change

• Bug fix (change which fixes an issue)
• New feature (change which adds functionality)
• Documentation update (improves or adds clarity to existing documentation)
• Other (chores, tests, code style improvements etc.)

Tested on

• iOS
• Android

Testing instructions

• To test the VAD streaming: run the VoiceActivityDetectionScreen within the Speech demo app.
• To test the VAD & STT integration: run the SpeechToTextScreen within the Speech demo app, with VAD toggle on.

Screenshots

Related issues

#1118

Checklist

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have updated the documentation accordingly
• My changes generate no new warnings

Additional notes

• Docs yet to be updated.
• Still investigating a rare issue of text vanishing before commitment in some unusual cases

[msluszniak]

Why these are in 10s of ms while other constants above are in miliseconds?

[IgorSwat]

All the constants in this file are in 10s of ms.

[msluszniak]

Then why these are named kWindowSizeMs and kHopLengthMs, this ms suffix almost screams to me: "This value is in milliseconds". If not, then I would be very surprised ;p