Cleanup: Remove importlib.invalidate_caches calls

[hoodmane]

It hasn't been needed since we brought in the patch that fixed the time functions on Emscripten:
emscripten-core/emscripten#18301

[hoodmane]

Hmm test fails without invalidate_caches. I suspect this is due to a bug in the IDBFS...

[ryanking13]

IIRC, there was a browser timer precision issue about this (#3311). But I guess it is worth to experiment again.

[hoodmane]

Well we fixed that with #3313. I think it would be good to remove this because if there are still time resolution problems, we would find out about them faster. Otherwise it's a bit confusing when users directly writing files can't import them but our package resolution system won't ever see problems like that.

[ryanking13]

But according to Roman's comment here: #3311 (comment), if the browser's timer precision is the problem, then mtime stored by emscripten won't be very accurate anyway as emscripten relies on browser APIs (Date.now()).

[hoodmane]

Well but to reproduce the problem, you need to

1. modify the directory
2. import from the directory
3. modify the directory again

All within a 1ms window, and then not modify the directory any further. Before we made this fix the window for triggering the problem was a full second. I just don't see that it's very likely to be a problem.

I guess what we should do that will make everyone happy is have the time functions always increment the current time by a nanosecond:

let lastTime;
let lastDelta = 0;
export function monotonicNanoseconds() {
  const now = Date.now();
  if (now === lastTime) {
    lastDelta++;
  } else {
    lastTime = now;
    lastDelta = 0;
  }
  return now * 1000 + lastDelta;
}

I think this will make it actually impossible to trigger problems with the importlib cache.

[ryanking13]

I just don't see that it's very likely to be a problem.

Yeah, actually, I was just thinking it may be a browser issue, not that I think it's a real cause. In any case, if the import works well without invalidate_caches(), this is definitely a big improvement, so thanks for working on this.