Function vad_simple 

pub fn vad_simple(
    pcmf32: &[f32],
    sample_rate: i32,
    last_ms: i32,
    vad_thold: f32,
    freq_thold: f32,
) -> bool

Energy-based VAD — port of common.cpp::vad_simple.

Returns true if the audio chunk is silence (no speech detected).