fix multi observe resolution, move dom settling to a method, eval passes

[jeremypress]

Why

we need evals that pass. in this example the demo button would resolve to multiple selectors on the page which you can't verify (you need one). We take the same naive approach we take with act that we'll take the first valid resolution of a selector. This can be improved later

What changed

1. take the first locator when observing
2. waitForDomSettled has to be called in user space for now. the callback we were using was not await-able. more on this later as this becomes a problem we need to squash.

Test plan

The eval passes now!