Add symbolic support for not

[pschanely]

Is your feature request related to a problem? Please describe.
At present, using the not operator realizes symbolic booleans - ideally, it would produce an inverted symbolic boolean. We haven't prioritized this because booleans often end up getting used in a conditional (or with short-circuiting "and"/"or"), where they'll need to be realized anyway. That said, symbolic negation would make our branch decision heuristics more accurate (for reasons that I won't get into here), so it might be worthwhile.

Describe the solution you'd like
The not operation sadly doesn't correspond to a special method (there is no __not__() method), so it's harder to intercept. But not impossible; we also intercept behavior at the opcode level, and that could be used to preserve the symbolic boolean.

[pschanely]

An implementation for this is in 340c669! Will close this out when it's released.