Fix: Packet typing based on stream and specify InputContainer.demux based on incoming stream

[ntjohnson1]

Resolves: #2133

• 2 commits specify the frames to confirm this fix works
• Make Packet Generic across tream types and allow specifying
  • Defaults to Stream on unqualified creation for backwards compatibility
• Update InputContainer.demux to make best effort at returning specialized packet variant type
• Test changes:
  • In test_streams I add data_packet Packet[DataStream] since we had a previous variable packet Packet[VideoStream]
  • In test_streams I add updated_streams since we know packet.stream is a VideoStream now but we cannot infer the type returned through stream_map which collects all the different stream types.