feat!(transport-quic): rework QUIC transport using transport framing

[rvolosatovs]

• Reuse a singular QUIC connection for invocations and serving, which eliminates the need for TLS handshake on each invocation
  • Use the same framing mechanism already used for TCP and UDS to facilitate that
• Increase default framing stream buffer sizes
• Fix decoding of pending stream<T> values
• Notify (async) readers on ingress stop
• Add ConnHandler trait to allow hooking into the async stream tear down procedure (which would be impossible in e.g. Drop, since that would take the values by &mut and we need to run things in an async runtime in a non-blocking fashion - https://docs.rs/quinn/latest/quinn/struct.SendStream.html#method.stopped is particularly tricky)
  • I think we can do better on the API front here, but it's a backwards-compatible stopgap, which works for now - the trait itself is marked experimental
  • Current design allows users to chose the "graceful" or best-effort "fire-and-forget" mode. Not sure yet if the latter has a valid use case, probably when this API is reworked, the "graceful" shutdown behavior should be forced