Rework internals - preparation for fragmentation

[ghost]

• improve setup payload handling to release it even if it not used, and allow to use it at client side both inside SetupFrame sending and inside acceptor
• simplify usage of flows with RequestStrategy
• rewrite streams to use one Map with FrameHandler instead of Map per Job, Limiter and Channel
  • FrameHandler is an abstraction over stream, which handles all kind of frames for specific frame + handles request life-cycle
  • in next PR it will also handle reassembling of frames
• remove several hacks needed for K/N
• change scopes used for requests/connection lifecycle - this will be improved for customization in next PR

[yschimke]

Won't progress on further reviews until #175 lands

[yschimke]

I can't give a meaningful review of this, it's big and requires understanding of where you are heading. Tests are quite good, so LGTM.