Support for a binary Websocket protocol

Kallichore's Websocket protocol is modeled after that of the Jupyter kernel gateway; that is, it sends text messages over the websocket that are well-formed JSON.

{
    "channel": "iopub",
    "header": {
        "msg_type": "example"
    },
    "content": {
        "example": true
    }
}

This text-based representation has a few upsides:

• it makes debugging a lot easier since you can examine the message and its contents as simple strings
• it makes it easier to compose valid socket messages using high-level tools and in test frameworks

However, it also has a few downsides:

• it is not very space efficient
• it is unfriendly to raw binary data such as the message buffers (which we are currently base64 encoding)
• it is slightly more computationally expensive since everything needs to be serialized on the backend and then parsed on the front end

For these reasons, the official Jupyter Server uses a binary-based WebSocket protocol. We could support exactly the same one, as an option, if needed:

https://jupyter-server.readthedocs.io/en/latest/developers/websocket-protocols.html

Start with the Jupyter Server binary WebSocket protocol documentation linked in the issue, then locate Kallichore’s current text/JSON WebSocket implementation. Define whether binary mode is optional and how it handles raw buffers, and add coverage demonstrating protocol compatibility before considering the work done. No repository files or tests are named in the issue.