What?
Adds a metrics function to "next/server", in the style of headers, to set arbitrary metrics adhering to the server timing spec.

Why?
I wanted to return metrics about the time consumed on each query executed on server actions.

How?
Added a serverTimingAsyncStorage which will wrap the execution of the server action, then inside the server action you can do:

import { metrics } from "next/server";
export async function getData() {
  const m = metrics();
  const time = performance.now();
  const users = await db.getUsers();
  m.set("db", {dur: performance.now() - time, desc: "getUsers"});
  return users;
}