feat: 新增 Amlogic AMLENC 硬件编码支持

- 新增动态加载及 ABI 校验的 AMLENC H.264/H.265 编码器
- 注册 Amlogic 后端并扩展编码器自检
- 并行执行 MJPEG 解码与 AMLENC 编码
- 复用 NV12 缓冲区并移除冗余帧初始化
- 优化低延迟帧分发及 RTCP 关键帧恢复
- 动态调整 AMLENC 码率尚未完成，效果不佳

src/video/codec/h264.rs

@@ -48,6 +48,8 @@ pub enum H264EncoderType {
     Rkmpp,
     /// V4L2 M2M (ARM generic) - requires hwcodec extension
     V4l2M2m,
+    /// Amlogic S912/GXM AMLENC
+    Amlogic,
     /// Software encoding (libx264/openh264)
     Software,
     /// No encoder available
@@ -64,6 +66,7 @@ impl std::fmt::Display for H264EncoderType {
             H264EncoderType::Vaapi => write!(f, "VAAPI"),
             H264EncoderType::Rkmpp => write!(f, "RKMPP"),
             H264EncoderType::V4l2M2m => write!(f, "V4L2 M2M"),
+            H264EncoderType::Amlogic => write!(f, "AMLENC"),
             H264EncoderType::Software => write!(f, "Software"),
             H264EncoderType::None => write!(f, "None"),
         }
@@ -80,6 +83,7 @@ impl From<EncoderBackend> for H264EncoderType {
             EncoderBackend::Vaapi => H264EncoderType::Vaapi,
             EncoderBackend::Rkmpp => H264EncoderType::Rkmpp,
             EncoderBackend::V4l2m2m => H264EncoderType::V4l2M2m,
+            EncoderBackend::Amlogic => H264EncoderType::Amlogic,
             EncoderBackend::Software => H264EncoderType::Software,
         }
     }