hyper-spec evaluate_ruby should handle return of non-ruby objects

This breaks with maximum call stack exceeded for example:

evaluate_ruby "'Element[JS.call(:eval, "(function () { return window; })();")]'"

because this returns a native js object, which cannot be processed by ruby's to_json (which is used to convert the resulting objects)

what should happen if things break is to report back some kind of details on the object type that was the result of the expression.

(Note this may already be fixed or better behaved in the new experimental version of hyper-spec)