The serve-time socket handler object Bun expects under Bun.serve's
websocket option.
open(ws: BunServerWebSocket): void
Called once the socket is live.
message(ws: BunServerWebSocket,message: string | Uint8Array): void
Called per inbound frame.
close(): void
Called once on close.
error(ws: BunServerWebSocket,error: unknown): void
Called on transport error.