With Haxe 4 installed, I typed the following to fiddle with this library from a REPL:

~ haxelib install hxprng
~ haxelib run ihx
>> addlib hxprng

Then I tried importing PCG32 by typing both of the following:
import hxprng.PCG32;
import PCG32;

Neither of those worked. I think it's because the haxelib.json and classpath aren't configured right for Haxe 4's haxelib. I have forked and plan on fixing this.