ddc-core-flow: wind: only wind refs if we think it's inside the binding of a lowered process - that is, if there are forall Rates in the type of a bind
ddc-core-flow: when producing Process#, add named binder for the RateNats. this allows concretize pass to use these RateNats instead of rateOfSeries#
ddc-core-flow: rate inference: name RateNats: update tests