[lua] hxcoro with -D lua-vanilla

I asked Claude to make hxcoro work in lua-vanilla mode and it turns out not much is needed: https://github.com/HaxeFoundation/hxcoro/pull/175

With this I can indeed run its tests locally with lua 5.4 installed.

Obviously, I don't want to actually make the bitshift-related changes over there, so that's something we should look into here. The `now` adjustments also looks like something that could be adjusted over here.