Add a new "marker" trait that allows users to specify the order in which ops are verified.
By default: verify traits, then the op
When VerifyOpBeforeTraits is attached: verify op, then the traits
VerifyOpBeforeTraits is useful when an interface verifier calls an InterfaceMethod. Without VerifyOpBeforeTraits, the op was not verified yet (and could be broken), so calling an InterfaceMethod is dangerous and could crash.