function startKeepAlives(interval) {
            //=> Regularly send keep-alive SSE comments, clear interval on socket close
            const keepAliveTimer = setInterval(() => {
                return write(": sse-keep-alive\n");
            }, interval);
            //=> When the connection gets closed (close=client, finish=server), stop the keep-alive timer
            res.once("close", () => {
                return clearInterval(keepAliveTimer);
            });
            res.once("finish", () => {
                return clearInterval(keepAliveTimer);
            });
        }
Writes heartbeats at a regular rate on the socket.

@param {number} interval