Convert attribute hiding to something like what srvyr does?

[dcaseykc]

https://github.com/gergness/srvyr/blob/30ce0feb6a8801456046017762eacf4e537a4fa5/R/summarise.r

Hides the survey in an environment and pulls from there-- We could just stash sdes and stype there.

Or define an object type that passes things like [ to NextMethod after a bit of munging to make sure the _ids are held. TBD