feat: macOS VoiceProcessingIO for hardware AEC + delay-compensated NLMS

- Add --os-aec flag: uses Apple VoiceProcessingIO audio unit for
  hardware echo cancellation (same engine as FaceTime)
- New vpio feature + audio_vpio.rs: combined capture+playback via VPIO
- Improved software AEC: delay-compensated leaky NLMS with Geigel DTD
  (60ms tail, 40ms delay, configurable via --aec-delay)
- Add --aec-delay flag for tuning software AEC delay compensation
- Add dev-fast Cargo profile (opt-level 2 with incremental compilation)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/wzp-client/src/lib.rs

@@ -10,6 +10,8 @@
 pub mod audio_io;
 #[cfg(feature = "audio")]
 pub mod audio_ring;
+#[cfg(feature = "vpio")]
+pub mod audio_vpio;
 pub mod bench;
 pub mod call;
 pub mod drift_test;