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/call.rs

@@ -42,6 +42,9 @@ pub struct CallConfig {
     /// When enabled, only every 50th frame carries a full 12-byte MediaHeader;
     /// intermediate frames use a compact 4-byte MiniHeader.
     pub mini_frames_enabled: bool,
+    /// AEC far-end delay compensation in milliseconds (default: 40).
+    /// Compensates for the round-trip audio latency from playout to mic capture.
+    pub aec_delay_ms: u32,
     /// Enable adaptive jitter buffer (default: true).
     ///
     /// When true, the jitter buffer target depth is automatically adjusted
@@ -63,6 +66,7 @@ impl Default for CallConfig {
             noise_suppression: true,
             mini_frames_enabled: true,
             adaptive_jitter: true,
+            aec_delay_ms: 40,
         }
     }
 }
@@ -241,7 +245,7 @@ impl CallEncoder {
             block_id: 0,
             frame_in_block: 0,
             timestamp_ms: 0,
-            aec: EchoCanceller::new(48000, 30), // 30ms echo tail (laptop/phone)
+            aec: EchoCanceller::with_delay(48000, 60, config.aec_delay_ms),
             agc: AutoGainControl::new(),
             silence_detector: SilenceDetector::new(
                 config.silence_threshold_rms,