Add an option to introduce an artificial delay between iterations

[dead-claudia]

I'd like to migrate away from the unmaintained Benchmark.js to this, and while this has almost everything I need, I need a way to introduce artificial delay, because I want to make sure it's actually tracking a fresh new frame each time.

That uses a fairly arbitrary delay, but ideally, this delay would be a function so I could pass it a () => new Promise(resolve => requestAnimationFrame(resolve)) function instead (as that's what I really need in practice).

[jerome-benoit]

afterEach() hook is executed after each iteration.

[dead-claudia]

@jerome-benoit Oh, I missed that. Thanks!

Unfortunately, I went a different route anyways, since I'm also benchmarking on browsers and I have to contend with its reduced resolution (which can be as low as 1ms) and I needed a hard guarantee that I was getting accurate timings in spite of it.

Also turned out to be pretty simple to roll, the hard part only being nailing down the right math for when to halt the test (I'm using a 99% confidence interval at the moment).

[jerome-benoit]

tinybench works on browser. And I doubt the timestamping is made differently on JS benchmarking tools around there.

[dead-claudia]

Sorry, forgot to close.

@jerome-benoit I took a cursory glance in the code, and I suspect my listed concern isn't accounted for, but I'll need to walk through some math and collect a bunch of links before I can file a proper bug report. Edit: filed #143