lfs: avoid a potential variable reference before assignment error in cmdserver A coworker hit this once yesterday when pulling in thg (a retry worked), and then I hit it with strip after a pull. I had a difficult time recreating a test for this (at least one of the tricks was to not use '-R', which seems to cause reposetup() to be called for each command), so I'm not sure how large of a window there actually is for this. Calling reposetup() *after* the requirement is added will skip the hook entirely. The other issue I had was adding a couple `ui.status()` lines around the check that installs the hook. On Windows, the cmdserver process ballooned to 1.6GB and hung. Changing that to `ui.warn()` avoided the hang. It also hung on macOS, but without the large memory usage.

wireprotov2: establish dedicated classes for input and output streams Streams are unidirectional. As part of implementing encoding/decoding support, it became clear that it didn't make sense for a generic "stream" class to hold functionality related to both encoding and decoding. So we create new classes to represent the flavor of stream. Differential Revision: https://phab.mercurial-scm.org/D4920

wireprotov2: pass ui into clientreactor and serverreactor This will allow us to use config options to influence compression settings. Differential Revision: https://phab.mercurial-scm.org/D4919

wireprotov2: handle stream encoding settings frames Like what we just did for the server reactor, we teach the client reactor to handle stream encoding settings frames. The code is very similar. We define a method on the stream class to handle processing the data within the decoded frames. However, it doesn't yet do anything useful. Differential Revision: https://phab.mercurial-scm.org/D4918

wireprotov2: document client reactor actions We should document these so consumers have an easier life. Differential Revision: https://phab.mercurial-scm.org/D4917

wireprotov2: handle sender protocol settings frames We teach the server reactor to handle the optional sender protocol settings frames, which can only be sent at the beginning of frame exchange. Right now, we simply decode the data and record the sender protocol settings on the server reactor instance: we don't yet do anything meaningful with the data. Differential Revision: https://phab.mercurial-scm.org/D4916

wireprotov2: update stream encoding specification The encoding of data within streams in the frame-based protocol is not yet defined or implemented. This means that all data in wire protocol version 2 is currently being sent out raw, without compression. That's obviously not ideal. This commit formalizes the beginnings of stream encoding support in the protocol. I suspect we'll change behavior substantially in the future. My goal is to get something landed so we can use compression. We can build out more robust support later. Because the frame type ID changed, this is strictly BC. But existing code wasn't using the frame. I'll bump the framing protocol version later once code is introduced to use the new frame. Differential Revision: https://phab.mercurial-scm.org/D4915

cborutil: cast bytearray to bytes This code didn't like passing in bytearray instances. Let's cast bytearray to bytes so it works. Differential Revision: https://phab.mercurial-scm.org/D4914

tests: disable zstd in test This makes the test pass in pure installs. Differential Revision: https://phab.mercurial-scm.org/D4913

wireprotov2: remove "compression" from capabilities response This is not used. And future commits will change how this mechanism works. Let's remove it. As a bonus, this fixes some test failures on pure installs (due to zstd references). Differential Revision: https://phab.mercurial-scm.org/D4912