net/quinn: Support stream multiplexing

• net/quinn: Add helper for adding stream id as meta to buffers
• net/quinn: Add helper for queries
• net/quinn: Add quinnquicmux to support stream multiplexing
• net/quinn: Support stream multiplexing in quinnquicsink
• net/quinn: Add quinnquicdemux to support stream demultiplexing
• net/quinn: Handle multiple stream connections in quinnquicsrc
  While at it, use PushSrc as base class. quinnquicsrc never supported seeking and only ever operated in push mode. Length and offset for create from BaseSrc was also never really honoured. Use PushSrc as the base class which is more appropriate.

Depends on !1613 (merged).

Closes #541.

Some code for testing can be found here.