Closes #2858

We need to track both the names of nullary operators in scope and whether or not
we in are in the scope of the `q::init` operator. The latter is require
so that we can ensure all assignments in the init operator are unprimed.
So we expand the reader to store both these bits of data

Closes #2863

Fixes an incorrect translation that was translating initialization of
state variables in quint init predicates into assignments, when they
should only be equalities.