wireproto: support for receiving multiple requests Now that we have request IDs on each frame and a specification that allows multiple requests to be issued simultaneously, possibly interleaved, let's teach the server to deal with that. Instead of tracking the state for *the* active command request, we instead track the state of each receiving command by its request ID. The multiple states in our state machine for processing each command's state has been collapsed into a single state for "receiving commands." Tests have been added so our branch coverage covers all meaningful branches. However, we did lose some logical coverage. The implementation of this new feature opens up the door to a server having partial command requests when end of input is reached. We will probably want a mechanism to deal with partial requests. For now, I've tracked that as a known issue in the class docstring. I've also noted an abuse vector that becomes a little bit easier to exploit with this feature. Differential Revision: https://phab.mercurial-scm.org/D2870