feat: jitter buffer instrumentation — drift test, telemetry, parameter sweep

WZP-P2-T1-S1: Automated drift measurement
- New drift_test.rs: DriftTestConfig, DriftResult, run_drift_test()
- CLI --drift-test <secs>: sends tone, measures actual vs expected duration
- Interpretation tiers: EXCELLENT (<50ms) / GOOD / FAIR / POOR
- 2 unit tests: drift math verification, config defaults

WZP-P2-T1-S2: Jitter buffer telemetry
- JitterStats gains: total_decoded, underruns, overruns, max_depth_seen
- JitterBuffer: record_underrun(), record_decode(), reset_stats()
- CallDecoder: stats() getter, reset_stats()
- JitterTelemetry: periodic tracing::info! logger with configurable interval
- 4 unit tests: ingestion tracking, underrun tracking, reset, interval

WZP-P2-T1-S3: Parameter sweep
- New sweep.rs: SweepConfig, SweepResult, run_local_sweep()
- Tests 20 jitter buffer configs (5 target × 4 max depths) locally
- CLI --sweep: runs sweep, prints ASCII comparison table
- No network needed — pure encoder→decoder pipeline test
- 3 unit tests: config defaults, local sweep runs, table formatting

216 tests passing across all crates.

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

crates/wzp-client/src/echo_test.rs

@@ -266,7 +266,7 @@ pub async fn run_echo_test(
         }
     }
 
-    let jitter_stats = decoder.jitter_stats();
+    let jitter_stats = decoder.stats().clone();
     let total_frames_received = recv_pcm.len() as u64 / FRAME_SAMPLES as u64;
     let overall_loss = if total_frames > 0 {
         (1.0 - total_frames_received as f32 / total_frames as f32) * 100.0