perf: check for divisibility by small primes

[ForbesLindesay]

In my tests, this results in the prime searching process running approximately twice as fast. I believe this happens because:

1. A very large proportion of the candidates can be eliminated by checking them for divisibility with the first 2,000 primes.
2. Checking against the first 2,000 primes is very fast, even when single threaded in JavaScript.
3. Calling out to OpenSSL via the terminal adds considerable overhead/latency

Benchmarks on the sample image (higher is better)

The old code that always uses OpenSSL

36.7 prime candidates tested per second
37.5 prime candidates tested per second
33.7 prime candidates tested per second

My version that first checks for divisibility by small primes

60.5 prime candidates tested per second
86.5 prime candidates tested per second
95.6 prime candidates tested per second

[TotalTechGeek]

Oh cool! I'll try to benchmark & potentially merge this later!

That makes perfect sense! OpenSSL also implements trial divisions, which is why I didn't think it'd be worth it, but this is cool! :)

[ForbesLindesay]

I'm also going to have a go at using node.js worker_threads with all the prime testing code in node.js and see how that compares to calling openSSL, but thought this was worth sharing while I look into that.