Node.js — Cancel Slow Work with AbortController

tinyserve can fetch an update from several mirrors. Asking all of them and keeping the fastest is
easy; what separates a robust version from a leaky one is cancelling the others, and giving
up when everyone is too slow. Node uses the web's
[`AbortController`](https://nodejs.org/api/globals.html#class-abortcontroller) for that:
fetch, fs.readFile, timers/promises, child_process, streams and events.once all
accept a signal.

Your task

Write async fastestMirror(mirrors, timeoutMs, download):

• Call download(mirror, { signal }) for every mirror at once. It returns a promise of the

mirror's data, rejects if the mirror is down, and rejects with an AbortError as soon as
signal aborts.

• Resolve with the first successful download. A mirror that is down does not win.
• Once there is a winner, abort every download still running.
• If nothing succeeded after timeoutMs, abort everything and reject with a TimeoutError

(error.name === 'TimeoutError').

• If every mirror fails before the deadline, reject with the AggregateError of

[`Promise.any`](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Promise/any).

The driver reports the result (or the error's name) and which downloads were aborted while
still running.

Tools

• AbortSignal.timeout(ms) — a signal that aborts by itself with a TimeoutError.
• AbortSignal.any([a, b]) — aborts when any of the signals aborts (Node 20.3+).
• signal.reason — what it was aborted with.