Negative Trace Literals

[DavePearce]

Minimal example for reproduction:

(module test)
(defcolumns A B)
(defconstraint test () (vanishes! (+ A B)))

With this trace:

{ "test": { "A": [-1], "B": [1] } }

Passes corset check -eeee, but crashes with corset check -eeeeN. Clearly converting the negative number into a field element is causing the problem. However, we actually could do something sensible here and that would be helpful for testing.