SAWCore environment needs to be scoped in SAWScript

[sauclovian-g]

Currently pending changes (#2720) fix the long-term problem that the Cryptol environment in the SAWScript interpreter isn't scoped (#2304); however, that exposes a deeper and more obscure problem that the SAWCore environment isn't scoped either.

For the time being the SAWCore library does not expose a sound way to roll back to an earlier state, and because it has internal state hacking it by copying the whole thing (as I did with the Cryptol environment for a first cut) doesn't work.

Note that test03.saw in test2304 exhibits the problem; unless there turn out to be further internal ramifications, there may not be any real need for additional tests just for this issue.