fix: retain bounds tightening on quantifier decls during symbol resolution

We were inadvertently taking a copy of the quantifier's decl's type, modifying
the copy, then discarding it. As a result, the tightening of the bounds on a
range would not take effect. The user-visible outcome of this was that the value
type logic would infer a larger C type than necessary to hold scalar values
(e.g. int64_t when it only needed int8_t).

Github: closes #181 "quantifier range refinement gets lost"