chore(video): sample decoded frames periodically

crates/wzp-video/src/decoder.rs

@@ -12,4 +12,9 @@ pub trait VideoDecoder: Send {
     /// Returns `Ok(Some(frame))` when a frame is ready, `Ok(None)` if more
     /// data is needed (e.g., for reordering), or an error.
     fn decode(&mut self, access_unit: &[u8]) -> Result<Option<VideoFrame>, VideoError>;
+
+    /// Compact implementation-specific state useful for field diagnostics.
+    fn debug_snapshot(&self) -> Option<String> {
+        None
+    }
 }