AAC: merge `VmInternalError::InvariantViolation` and `VmInternalError::Except`

[Jiloc]

Both variants indicate that an unexpected condition happened. Once the AAC testing framework is done and can be used to validate that the change didn't cause a consensus bug, merge those two variants

https://github.com/Jiloc/stacks-core/blob/b20d3672696bbfc817430a526982bed8f243ac14/clarity-types/src/errors/mod.rs#L78