Update model plumbing for Rust example

The v6.2 models broke the Rust example. Update the logic for driving
them to reflect what the reference Python code does.

Fixes: #745
Co-Authored-By: Claude <noreply@anthropic.com>

examples/rust-example/src/utils.rs

@@ -36,7 +36,7 @@ pub struct VadParams {
 impl Default for VadParams {
     fn default() -> Self {
         Self {
-            frame_size: 64,
+            frame_size: 32,  // 32ms for 512 samples at 16kHz
             threshold: 0.5,
             min_silence_duration_ms: 0,
             speech_pad_ms: 64,