Add queryFirstWithTraits

[mdirolf]

This is mostly just a proof of concept - obviously doesn't make sense unless you're satisfied with the api @krispya

[mdirolf]

I added readFirst to QueryResults just to make this easier to implement. If preferable we could ditch the queryFirstWithTraits part and just stick with readFirst only. If you think it's better could also potentially change the readFirst return type to match a bit closer to the callback params for readEach (i.e. [ [...traits], Entity] | [[...undefined], undefined]).

LMK if either of those are preferable to this and I'd be happy to change this PR to match.