- Unreference the async handle to allow the loop to stop without walking first
- Wait before walking open handles to allow earlier uv_close calls to complete
- Moved things that have loop affinity to KestrelThread like
WriteReqPool, MemoryPool and the ConnectionManager
- Changed on the listeners to only kill the ListenSocket, not the
connections on dispose
- Moved connection disposal to KestrelThread.Stop
- Simplify the connection manager logic so it's possible to walk and
wait in a single call