SD card sync with on-device VAD

[beastoin]

As a user, I want a better, faster SD card sync experience.

Key results:

• App: Use on-device VAD (Voice Activity Detection) to trim audio bytes before storing them in the app.
• App: Sync larger batches of audio (e.g., up to 10 hours of audio) from the SD card to the app before syncing to the backend.

Refs:

• Related Issue 1650 , 518
• App's SD card's Sync: https://github.com/BasedHardware/omi/blob/main/app/lib/services/wals.dart#L148

[chiragksharma]

Can we use the tflite-micro with the XiAo nrf52840 as given in the seeedStudio docs for the on-device VAD ?