perf(video): 改善视频卡顿问题并优化编码性能

改善内容:
1. NAL单元duration累积bug修复
   - 修改video_track.rs和unified_video_track.rs
   - 只有帧内最后一个NAL获得frame_duration,其他为ZERO
   - 确保同一帧的所有NAL共享相同的RTP时间戳

2. 修复VP8/VP9固定1秒duration错误
   - 将Duration::from_secs(1)改为正确的frame_duration计算

3. PTS计算优化(shared_video_pipeline.rs)
   - 将pipeline_start_time从Mutex<Option<Instant>>改为AtomicI64
   - 消除每帧一次的async mutex lock
   - 使用compare_exchange实现无锁的首帧时间设置

4. 避免重复读取config
   - 在encode_frame中缓存fps,避免末尾再次获取config锁

5. 编码器零拷贝优化
   - H264/H265/VP8/VP9编码器使用drain()替代clone()
   - 减少内存分配和拷贝开销

6. MJPEG处理器优化
   - 无客户端时跳过JPEG编码(WebRTC-only模式优化)

7. RKMPP YUYV直接输入支持
   - hwcodec C++层添加YUYV422格式支持
   - H264编码器添加Yuyv422输入格式选项

src/webrtc/video_track.rs

@@ -484,17 +484,25 @@ impl UniversalVideoTrack {
     }
 
     /// Send NAL units as samples (H264 only)
+    ///
+    /// Important: Only the last NAL unit should have the frame duration set.
+    /// All NAL units in a frame share the same RTP timestamp, so only the last
+    /// one should increment the timestamp by the frame duration.
     async fn send_nals(&self, nals: Vec<Bytes>, is_keyframe: bool) -> Result<()> {
         let mut total_bytes = 0u64;
         // Calculate frame duration based on configured FPS
         let frame_duration = Duration::from_micros(1_000_000 / self.config.fps.max(1) as u64);
+        let nal_count = nals.len();
 
         match &self.track {
             TrackType::Sample(track) => {
-                for nal_data in nals {
+                for (i, nal_data) in nals.into_iter().enumerate() {
+                    let is_last = i == nal_count - 1;
+                    // Only the last NAL should have duration set
+                    // This ensures all NALs in a frame share the same RTP timestamp
                     let sample = Sample {
                         data: nal_data.clone(),
-                        duration: frame_duration,
+                        duration: if is_last { frame_duration } else { Duration::ZERO },
                         ..Default::default()
                     };