Responsible for managing a WebSocket connection, either as a server or as a client.

Owns:

• a url for where to listen, or connect to
• a state machine (server/client/connecting/closed etc)
• an AbortController for when "closed" state is desired or reached
• a Set, per channel name
• a WebSocketServer (when server)
• a WebSocket (when client)
• yet undelivered messages

Emits:

• "close" when aborted or closed
• WebSocketBroadcastChannel: "message" to deliver messages locally to WebSocketBroadcastChannels

Listens to:

• AbortController: "abort" → state:closed.
• WebSocketBroadcastChannel: "close" → remove from channelSets, and if empty, abort.
• WebSocketBroadcastChannel: "postMessage" → means a message came from a WebSocketBroadcastChannel, so it should be sent to the server or clients, depending on the state.
• WebSocketServer when in state:server: "client:open" → sendOutgoingMessages
• WebSocketServer when in state:server: "client:message" → means a message came from a client, so it should go to all WebSocketBroadcastChannels in channelSets for the message's channel name, and to all server.webSockets.
• WebSocketServer when in state:server: server.finished → state:client
• WebSocket when in state:client: "open" → sendOutgoingMessages
• WebSocket when in state:client: "message" → means a message came from the server, so it should go to all WebSocketBroadcastChannels in channelSets for the message's channel name.
• WebSocket when in state:client: "close" → state:client closed
• WebSocket when in state:client: "error" → state:client closed