AV1Packet incompatible with sample builder

When trying to use `AV1Packet` as a depacketiser I get an error...

```
cannot use &(codecs.AV1Packet literal) (value of type *"github.com/pion/rtp/codecs".AV1Packet) as "github.com/pion/rtp".Depacketizer value in assignment: *"github.com/pion/rtp/codecs".AV1Packet does not implement "github.com/pion/rtp".Depacketizer (missing method IsPartitionHead)
```