Http3Connection only handles common elements:
     - holds control and qpack streams,
     - holds a HashMap of active transactions,
     - holds the Http3State of a http3 connection,
     - performs sending data for control, qpack and transaction streams,
     - handles decoding of new unidi streams(the client/server handlers differ in how they handle a  Push streams, therefore handle_new_unidi_stream returns if a stream was a push stream and the client/server handler consume them appropriately),
     - handles streams reading (this function may return that a stream is a push stream or a list of control frames to be handle by the client/server handler)

    The client/server handlers:
     - holds a base_handler(Http3Connection)
     - http3 events
     - neqo_transport::Connection (this is only for the client)
     - process_htttp3 has been moved from Http3Connection to the client/server handlers,
     - also check_connection_events which iterates through ConnectionEvents and calls handlers for the events (handlers are implemented in Http3Connection or in the client/server handlers)